SEARCH · Search PubMed

Results for “Decarboxylation”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 37 records · Page 2Linked to original sources

PubMed1986

Acetylation of decarboxylated S-adenosylmethionine by mammalian cells.

Decarboxylated S-adenosylmethionine was found to be a substrate for the nuclear acetyltransferases that act on polyamines and on histones. The rate of acetylation of decarboxylated S-adenosylmethionine was more than twice that of spermidine at saturating substrate concentrations, and decarboxylated S-adenosylmethionine was an active inhibitor of the acetylation of histones by nuclear extracts from rat liver. The acetylation of decarboxylated S-adenosylmethionine occurred in vivo in SV-3T3 cells exposed to the ornithine decarboxylase inhibitor 2-(difluoromethyl)ornithine. The decline in putrescine and spermidine brought about by exposure to 2-(difluoromethyl)ornithine was found to be accompanied by a large rise in the content of both decarboxylated S-adenosylmethionine and acetylated decarboxylated S-adenosylmethionine. These results indicate that decarboxylated S-adenosylmethionine is metabolized not only in the well-known reactions in which it serves as an aminopropyl donor for polyamine biosynthesis but also by acetylation in reaction with acetyl coenzyme A. Furthermore, the inhibition of histone acetylation by decarboxylated S-adenosylmethionine could contribute to the biological effects brought about by inhibitors of ornithine decarboxylase.

Acetyl Coenzyme A↗

PubMed1996

Effect of Cold Hardening on the Components of Respiratory Decarboxylation in the Light and in the Dark in Leaves of Winter Rye.

In the dark, all decarboxylation reactions are associated with the oxidase reactions of mitochondrial electron transport. In the light, photorespiration is also active in photosynthetic cells. In winter rye (Secale cereale L.), cold hardening resulted in a 2-fold increase in the rate of dark respiratory CO2 release from leaves compared with nonhardened (NH) controls. However, in the light, NH and cold-hardened (CH) leaves had comparable rates of oxidase decarboxylation and total intracellular decarboxylation. Furthermore, whereas CH leaves showed similar rates of total oxidase decarboxylation in the dark and light, NH leaves showed a 2-fold increase in total oxidase activity in the light compared with the dark. Light suppressed oxidase decarboxylation of end products of photosynthesis 2-fold in NH leaves and 3-fold in CH leaves in air. However, in high-CO2, light did not suppress the oxidase decarboxylation of end products. Thus, the decrease in oxidase decarboxylation of end products observed in the light and in air reflected glycolate-cycle-related inhibition of tricarboxylic acid cycle activity. We also showed that the glycolate cycle was involved in the decarboxylation of the end products of photosynthesis in both NH and CH leaves, suggesting a flow of fixed carbon out of the starch pool in the light.

Journal Article↗

PubMed1984

Nonenzymatic decarboxylation of pyruvate.

Triton X-100, retinol, retinoic acid, retinal, hexane, dithiothreitol, mercaptoethanol, and some other commercially available chemicals caused nonenzymatic decarboxylation of pyruvate and alpha-ketoglutarate. "Lipids" obtained from human or pigeon liver homogenates using isopropanol/hexane also had very high nonenzymatic decarboxylating activity on these two alpha-ketoacids; most of this activity could be traced to the hexane (Eastman) used in the extraction. Optimum pH of the reaction with dithiothreitol and mercaptoethanol was 7-8 and with the other chemicals around 10, but considerable activity was present at pH 7-8. Liver homogenates had a scavenger effect on the decarboxylating activity of Triton X-100 and of dithiothreitol. Dithiothreitol and mercaptoethanol at high concentrations (greater than 1 mM) also had a scavenger effect on the decarboxylating activity of the "lipids." Pretreatment of Triton X-100, dithiothreitol, retinol, and the "lipids" with catalase markedly decreased the decarboxylating activity, while treatment with boiled catalase failed to do so. The results suggest that these compounds contain oxidizing contaminants, perhaps peroxide derivatives. Powerful oxidizing impurities have been reported in Triton X-100 from various sources by Y. Ashani and G. N. Catravas (1980, Anal. Biochem 109, 55-62). Such peroxide derivatives may cause nonenzymatic decarboxylation of pyruvate and alpha-ketoglutarate, presumably by a mechanism similar to the well-known nonenzymatic decarboxylation of alpha-ketoacids by hydrogen peroxide. In the absence of catalase and/or other protective agents against reactive oxygen derivatives, these chemicals would interfere in the assays of pyruvate dehydrogenase, pyruvate dehydrogenase complex, and alpha-ketoglutarate dehydrogenase complex which depend on the release of 14CO2 from alpha[1-14C]ketoacids.

Animals↗

PubMed1990

L-methionine decarboxylase from Dryopteris filix-mas: purification, characterization, substrate specificity, abortive transamination of the coenzyme, and stereochemical courses of substrate decarboxylation and coenzyme transamination.

L-Methionine decarboxylase from the male fern Dryopteris filix-mas has been purified 256-fold from acetone powder extracts to very near homogeneity. The enzyme is membrane-associated and requires detergent for solubilization during the initial extraction. The enzyme is a homodimer of subunit Mr 57,000 and shows a pH optimum at approximately 5.0 with 20 mM (2S)-methionine as substrate. The specific activity, kcat, for methionine is approximately 50 mol s(-1) (mol of active site)(-1) at pH 4.5 and below. A wide range of straight- and branched-chain (2S)-alkylamino acids are substrates for the enzyme. The values for the rate of decarboxylation, Vmax, and for the apparent Michaelis constant, Km, however, vary with structure and with the chirality at C-3. The pH dependence of V and V/K has been examined for three substrates: (2S)-methionine, valine, and leucine. Pyridoxal 5'-phosphate (PLP) is required for activity, and in the absence of excess PLP, the activity of the enzyme in incubations reduced with respect to time. The addition of PLP fully restores the activity, indicating that an abortive decarboxylation-transamination accompanies the normal decarboxylation reaction. The occurrence of the abortive reaction was confirmed by showing that [35S]methionine is converted to labeled 3-(methylthio)propionaldehyde while [4'-3H]PLP is converted to labeled pyridoxamine 5'-phosphate (PMP). The decarboxylation of (2S)-methionine gave 3-(methylthio)-1-aminopropane. Preparation of the N-camphanamide derivative of the amine allowed the C-1 methylene protons to be distinguished by 1H NMR spectroscopy. Synthetic samples of the camphanamide were prepared in which each of the C-1 methylene protons was replaced by deuterium. When (2S)-methionine and the C-2 deuteriated isotopomer were incubated with the enzyme in deuterium oxide and protium oxide, respectively, and the products were converted to their camphanamide derivatives and analyzed by 1H NMR spectroscopy, it was evident that decarboxylation occurred with retention of configuration at C-2. When the decarboxylation of six other substrates was studied, examination of the N-camphanamide derivatives of the amines indicated that decarboxylation occurred stereospecifically and, by analogy, with retention of configuration at C-2. When tritiated pyridoxal phosphate was incubated with the enzyme, tritiated pyridoxamine phosphate was formed. Analysis of the chirality of the methylene group at C-4' indicated that, during abortive transamination, protonation occurred from the 4'-si face of the coenzyme, the same stereochemical result as that obtained for several bona fide transaminase enzymes.(ABSTRACT TRUNCATED AT 400 WORDS)

Carboxy-Lyases↗

PubMed2004

C2-alpha-lactylthiamin diphosphate is an intermediate on the pathway of thiamin diphosphate-dependent pyruvate decarboxylation. Evidence on enzymes and models.

Thiamin diphosphate (ThDP)-dependent decarboxylations are usually assumed to proceed by a series of covalent intermediates, the first one being the C2-trimethylthiazolium adduct with pyruvate, C2-alpha-lactylthiamin diphosphate (LThDP). Herein is addressed whether such an intermediate is kinetically competent with the enzymatic turnover numbers. In model studies it is shown that the first-order rate constant for decarboxylation can indeed exceed 50 s(-1) in tetrahydrofuran as solvent, approximately 10(3) times faster than achieved in previous model systems. When racemic LThDP was exposed to the E91D yeast pyruvate decarboxylase variant, or to the E1 subunit of the pyruvate dehydrogenase complex (PDHc-E1) from Escherichia coli, it was partitioned between reversion to pyruvate and decarboxylation. Under steady-state conditions, the rate of these reactions is severely limited by the release of ThDP from the enzyme. Under pre-steady-state conditions, the rate constant for decarboxylation on exposure of LThDP to the E1 subunit of the pyruvate dehydrogenase complex was 0.4 s(-1), still more than a 100-fold slower than the turnover number. Because these experiments include binding, decarboxylation, and oxidation (for detection purposes), this is a lower limit on the rate constant for decarboxylation. The reasons for this slow reaction most likely include a slow conformational change of the free LThDP to the V conformation enforced by the enzyme. Between the results from model studies and those from the two enzymes, it is proposed that LThDP is indeed on the decarboxylation pathway of the two enzymes studied, and once LThDP is bound the protein needs to provide little assistance other than a low polarity environment.

Acetaldehyde↗

PubMed1982

The role of biotin and sodium in the decarboxylation of oxaloacetate by the membrane-bound oxaloacetate decarboxylase from Klebsiella aerogenes.

The biotin-containing oxaloacetate decarboxylase from Klebsiella aerogenes catalyzed the Na+-dependent decarboxylation of oxaloacetate to pyruvate and bicarbonate (or CO2) but not the reversal of this reaction, not even in the presence of an oxaloacetate trapping system. The enzyme catalyzed an avidin-sensitive isotopic exchange between [1-14C]pyruvate and oxaloacetate, which indicated the intermediate formation of a carboxybiotin enzyme. Sodium ions were not required for this partial reaction, but promoted the second partial reaction, the decarboxylation of the carboxybiotin enzyme, thus accounting for the Na+ requirement of the overall reaction. Therefore, the 14CO2-enzyme which was formed upon incubation of the decarboxylase with [4-15C]oxaloacetate, could only be isolated if Na+ ions were excluded. Preincubation of the decarboxylase with avidin also prevented its labelling with 14CO2. The isolated 14CO2-labelled oxaloacetate decarboxylase revealed the following properties. It was slowly decarboxylated at neutral pH and rapidly upon acidification. The 14CO2 residues of the 14CO2-enzyme could be transferred to pyruvate yielding [4-14C]oxaloacetate. In the presence of Na+ this 14CO2 transfer was repressed by the simultaneous decarboxylation of the 14CO2-enzyme. However, Na+ alone was insufficient as a cofactor for the decarboxylation of the isolated 14CO2-enzyme, since this required pyruvate in addition to Na+. It is therefore concluded that the decarboxylation of oxaloacetate proceeds over a CO2-enzyme--pyruvate complex and that free CO2-enzyme is an abortive reaction intermediate. The activation energy of the enzymic decarboxylation of oxaloacetate changed with temperature and was about 113 kJ below 11 degrees C, 60 kJ between 11 degrees C and 31 degrees C and 36 kJ between 31--45 degrees C.

Bacterial Proteins↗

PubMed1994

Mitochondrial function reflected by the decarboxylation of [13C]ketoisocaproate is impaired in alcoholics.

Mitochondria of patients with alcoholic liver disease exhibit structural abnormalities, and mitochondria isolated from animals exposed to ethanol are functionally deficient when studied in vitro. To assess possible functional consequences of these ethanol-associated alterations in vivo, we measured mitochondrial function in alcoholics noninvasively with a breath test. A mitochondrial function, the decarboxylation of ketoisocaproate (KICA), was assessed by measuring the exhalation of 13CO2 following the administration of 1 mg/kg 2-keto[1-13C]isocaproic acid, the decarboxylation of which occurs in mitochondria. The results of the KICA breath test in 12 alcoholic subjects were compared with the results in healthy controls and patients with nonalcoholic liver disease. The peak exhalation of 13CO2 and the fraction of the administered dose decarboxylated in 120 min were both significantly lower in alcoholics than in healthy controls and patients with nonalcoholic liver disease. In alcoholics, KICA decarboxylation was impaired in the presence of normal quantitative liver function tests such as the aminopyrine breath test and galactose elimination capacity, indicating that KICA decarboxylation does not simply reflect a decreased functional hepatic mass. The enrichment of circulating KICA with [13C]KICA was similar in alcoholics and controls, indicating that a decreased bioavailability or an increased dilution of labeled KICA cannot account for the decreased exhalation of 13CO2. It is concluded that mitochondrial function as reflected by KICA decarboxylation is impaired in chronic alcoholics. The functional impairment is specific for ethanol abuse and not a reflection of decreased global hepatic function. KICA decarboxylation could thus be useful as a marker for excessive ethanol consumption.

Adult↗

PubMed1964

OXALOACETATE DECARBOXYLATION AND OXALOACETATE-CARBON DIOXIDE EXCHANGE IN ACETOBACTER XYLINUM.

Benziman, Moshe (The Hebrew University of Jerusalem, Jerusalem, Israel), and N. Heller. Oxaloacetate decarboxylation and oxaloacetate-carbon dioxide exchange in Acetobacter xylinum. J. Bacteriol. 88:1678-1687. 1964.-Extracts of Acetobacter xylinum, prepared by sonic treatment, were shown to catalyze the decarboxylation of oxaloacetate (OAA) to pyruvate and CO(2), and the exchange of C(14)-carbon dioxide into the beta-carboxyl of OAA. Fractionation of the extracts with ammonium sulfate resulted in a 10-fold increase of the specific activity of the enzyme system catalyzing the CO(2) exchange and OAA decarboxylation reactions. The purified preparation catalyzed the exchange of pyruvate-3-C(14) into OAA. Similar pH curves with a pH optimum of 5.6 were obtained for the CO(2) exchange and OAA decarboxylation reactions. Both reactions require the presence of Mn(2+) or Mg(2+) ions. OAA decarboxylation was more strongly inhibited than the exchange of CO(2) by dialysis or metal-chelating agents. Avidin did not inhibit either reaction. Adenosine triphosphate (ATP), adenosine diphosphate (ADP), guanosine triphosphate (GTP), guanosine diphosphate (GDP), pyrophosphate, or inorganic phosphate did not promote OAA decarboxylation and the CO(2)-exchange reaction catalyzed by the purified preparation. The purified preparation failed to catalyze the carboxylation of phosphoenolpyruvate in the presence of GDP, ADP, or inorganic phosphate, and that of pyruvate in the presence of ATP or GTP, even when supplemented with an OAA-trapping system. A scheme for OAA decarboxylation which could account for the observed exchange reactions and for the failure to obtain net fixation of CO(2) is proposed. The relation between the exchange reaction and the synthesis of cellulose from pyruvate by A. xylinum is discussed.

Acetates↗

PubMed1981

Oxidative decarboxylation of free and peptide-linked amino acids in phagocytizing guinea pig granulocytes.

The oxidative decarboxylation of amino acids by a system consisting of myeloperoxidase-hydrogen peroxide-chloride has been demonstrated previously by others and the process has been considered to be part of the microbicidal armamentarium of some phagocytic leukocytes. We were able to translate these earlier observations, made on model systems, to intact guinea pig granulocytes. We could demonstrate differences in the cellular handling of peptide-linked amino acids as particles, compared with free amino acids. Specific inhibitors were used to explore two routes of oxidative decarboxylation: (a) the myeloperoxidase-catalyzed direct decarboxylation-deamination reaction, and (b) oxidation of alpha-keto acids after transamination of amino acids. These inhibitors were cyanide, azide, and tapazole for the former pathway, and amino-oxyacetate for the latter. Amino-oxyacetate profoundly inhibited the decarboxylation of free 14C-amino acids (alanine and aspartate) in both resting and stimulated cells, but had only a minimal effect on 14CO2 production from ingested insoluble 14C-protein. On the other hand, the peroxidase inhibitors cyanide, azide, and tapazole dramatically inhibited the production of 14CO2 from ingested particulate 14C-protein, but had only small effects on the decarboxylation of free amino acid. Soluble, uniformly labeled 14C-protein was not significantly converted to 14CO2 even in the presence of phagocytizable polystyrene beads. These observation suggest that the amino acids taken up by phagocytosis (e.g., as denatured protein particles) are oxidatively decarboxylated and deaminated in the phagosomes by the myeloperoxidase-hydrogen peroxide-chloride system; soluble free amino acids that enter the cytoplasm by diffusion or transport are oxidatively decarboxylated after transamination by the normal cellular amino acid oxidative pathway.

Amino Acids↗

PubMed1985

alpha-Ketobutyrate metabolism in perfused rat liver: regulation of alpha-ketobutyrate decarboxylation and effects of alpha-ketobutyrate on pyruvate dehydrogenase.

The oxidative decarboxylation and subsequent production of glucose from alpha-ketobutyrate were studied using perfused livers from fasted rats. The production of 14CO2 from alpha-keto-[1-14C]butyrate increased monotonically while the production of glucose from alpha-ketobutyrate was biphasic as the perfusate concentration of alpha-ketobutyrate was increased. The biphasic gluconeogenic response using alpha-ketobutyrate as the gluconeogenic precursor was similar to that observed with propionate. The decarboxylation of alpha-ketobutyrate was found to be exquisitely sensitive to the effects of the monocarboxylate transport inhibitor, alpha-cyanocinnamate. Infusion of beta-hydroxybutyrate caused a substantial inhibition of alpha-ketobutyrate decarboxylation while dichloroacetate, a pyruvate dehydrogenase kinase inhibitor, did not stimulate the metabolism of alpha-ketobutyrate but was inhibitory. The effects of alpha-ketobutyrate infusion on pyruvate decarboxylation were tested and it was found that at low perfusate pyruvate concentrations (ca. 0.25 mM) increasing alpha-ketobutyrate led to increasing inhibition of pyruvate decarboxylation, while at high perfusate pyruvate concentrations (ca. 2.5 mM) an initial inhibition was apparent which did not increase substantially with increasing alpha-ketobutyrate concentrations. The results obtained indicate that the regulation of alpha-ketobutyrate metabolism by oxidative decarboxylation differs significantly from that of pyruvate. In addition, while the rate of gluconeogenesis using alpha-ketobutyrate as a precursor was remarkably similar to that using propionate as a gluconeogenic precursor, the effects of alpha-ketobutyrate on the oxidative decarboxylation of pyruvate were qualitatively different from the effects of propionate on pyruvate metabolism.

Acetates↗

PubMed1993

Intramitochondrial distribution and transport of phosphatidylserine and its decarboxylation product, phosphatidylethanolamine. Application of pyrene-labeled species.

To investigate the mechanism of intramitochondrial translocation of phosphatidylserine and its decarboxylation product, phosphatidylethanolamine, the distribution of these lipids between the outer (OM) and inner (IM) mitochondrial membranes, as well as their transversal and lateral distribution in OM were studied. Fluorescent, pyrenyl derivatives of phosphatidylserine (PyrxPS) and phosphatidylethanolamine (PyrxPE) species were employed because they allow: (i), direct monitoring of PS (and PE) loading to the mitochondria; (ii) assay of PS decarboxylation by high-performance liquid chromatography with fluorescence detection and (iii), determination of the lateral distributions of PS and PE within the mitochondrial membranes. All PyrxPS species tested were efficiently decarboxylated by the solubilized decarboxylase and thus the distribution of the endogenous PE could be also studied. When the PyrxPS species were loaded to isolated mitochondria very little, if any, of the loaded PyrxPS or of the PyrxPE product was found in IM independent of the time and temperature of incubation, strongly suggesting that these lipids either never enter IM or their residence there is only transient. When mitochondria preloaded with Pyr4PS were incubated with an excess of acceptor vesicles in the presence of the lipid transfer protein, 80% of Pyr4PS and 30-40% of the Pyr4PE product were transported to the acceptor vesicles, indicating that at least corresponding fractions of these lipid were located in, or were in rapid equilibrium with the outer leaflet of OM. Since the decarboxylase is located in the inner membrane, these results signify that both PS and PE must be able to move readily across OM. Determination of the excimer to monomer ratio as the function of pyrenyl lipid concentration in mitochondria (i.e., OM) gave parallel results for PyrxPS and -PE species suggesting the lateral distribution of PS and PE in OM is similar and thus there is no specific enrichment of PS to the contact sites. To investigate the mechanism of PS transport from the outer leaflet to the decarboxylation site, the influence of PyrxPS hydrophobicity, i.e., pyrenylacyl chain length, on the rate of decarboxylation was determined. The variation of the length of the pyrenyl acyl chain from 4 to 12 carbons did not significantly affect the rate of PyrxPS decarboxylation in intact mitochondria, indicating that the transport of PS from the outer leaflet of OM to the site of decarboxylation takes place by lateral diffusion rather than by spontaneous or protein-mediated transport. The implications of these findings on the mechanism of intramitochondrial transport of PS and PE are discussed in terms of alternative models.

Animals↗

PubMed1982

Effect of inhibition of polyamine synthesis on the content of decarboxylated S-adenosylmethionine.

1. The content of decarboxylated S-adenosylmethionine (AdoMet) in transformed mouse fibroblasts (SV-3T3 cells) was increased 500-fold to about 0.4fmol/cell when ornithine decarboxylase was inhibited by alpha-difluoromethylornithine. This increase was due to the absence of putrescine and spermidine, which serve as substrates for aminopropyltransferases with decarboxylated AdoMet as an aminopropyl donor, and to the enhanced activity of AdoMet decarboxylase brought about by depletion of spermidine. The increase in decarboxylated AdoMet content was abolished by addition of putrescine, but not by 1,3-diaminopropane. 2. 5'-Methylthiotubercidin also increased decarboxylated AdoMet content, presumably by direct inhibition of aminopropyl-transferase activities, but the increase in its content and the decline in spermidine content were much less than those produced by alpha-difluoromethylornithine. 3. Decarboxylated AdoMet content of regenerating rat liver was measured in rats treated with inhibitors of ornithine decarboxylase. The content was increased by 60% 32h after partial hepatectomy in control rats, by 90% when alpha-difluoromethylornithine was given to the partially hepatectomized rats, and by 330% when 1,3-diaminopropane was used to inhibit putrescine and spermidine synthesis. After 48h of exposure to 1,3-diaminopropane, which completely prevented the increase in spermidine after partial hepatectomy, there was a 5-fold rise in hepatic decarboxylated AdoMet concentration. These increases were prevented by treatment with putrescine or with methylglyoxal bis(guanylhydrazone), an inhibitor of AdoMet decarboxylase. 4. These results show that changes in AdoMet metabolism result from the administration of specific inhibitors of polyamine synthesis. The possible consequences of the accumulation of decarboxylated AdoMet, which could, for example, interfere with normal cellular methylation or lead to depletion of cellular adenine nucleotides, should be considered in the interpretation of results obtained with such inhibitors.

Adenosylmethionine Decarboxylase↗

PubMed1983

Bacterial Decarboxylation of o-Phthalic Acids.

The decarboxylation of phthalic acids was studied with Bacillus sp. strain FO, a marine mixed culture ON-7, and Pseudomonas testosteroni. The mixed culture ON-7, when grown anaerobically on phthalate but incubated aerobically with chloramphenicol, quantitatively converted phthalic acid to benzoic acid. Substituted phthalic acids were also decarboxylated: 4,5-dihydroxyphthalic acid to protocatechuic acid; 4-hydroxyphthalic and 4-chlorophthalic acids to 3-hydroxybenzoic and 3-chlorobenzoic acids, respectively; and 3-fluorophthalic acid to 2-and 3-fluorobenzoic acids. Bacillus sp. strain FO gave similar results except that 4,5-dihydroxyphthalic acid was not metabolized, and both 3- and 4-hydroxybenzoic acids were produced from 4-hydroxyphthalic acid. P. testosteroni decarboxylated 4-hydroxyphthalate (to 3-hydroxybenzoate) and 4,5-dihydroxyphthalate but not phthalic acid and halogenated phthalates. Thus, P. testosteroni and the mixed culture ON-7 possessed 4,5-dihydroxyphthalic acid decarboxylase, previously described in P. testosteroni, that metabolized 4,5-dihydroxyphthalic acid and specifically decarboxylated 4-hydroxyphthalic acid to 3-hydroxybenzoic acid. The mixed culture ON-7 and Bacillus sp. strain FO also possessed a novel decarboxylase that metabolized phthalic acid and halogenated phthalates, but not 4,5-dihydroxyphthalate, and randomly decarboxylated 4-hydroxyphthalic acid. The decarboxylation of phthalic acid is suggested to involve an initial reduction to 1,2-dihydrophthalic acid followed by oxidative decarboxylation to benzoic acid.

Journal Article↗

PubMed2000

Metabolism of tryptophan in the liver: interference with decarboxylation of other aromatic amino acids.

Decarboxylation of aromatic amino acid in mammalian tissues is catalyzed by aromatic amino acid decarboxylase (EC. 4.1.1.28, AAD). The enzyme differs in its affinity to individual aromatic amino acids, the best substrates being 3,4-dihydroxyphenylalanine (dopa) and 5-hydroxytroptophan. Surprisingly, AAD is abundant in the liver, where the substrates with rather low affinity to AAD as tryptophan, phenylalanine, and tyrosine are offered to decarboxylation. In the present paper, the possibility of interference of tryptophan with decarboxylation of phenylalanine, tyrosine as well as dopa in the liver was investigated. The AAD activity was measured radiometrically with 1-14C-labeled aromatic amino acid substrates using the rat liver enzyme. The influence of tryptophan on decarboxylation of tyrosine was formally competitive with Ki = 9.2 x 10(-3) M, while the inhibition of decarboxylation of phenylalanine by tryptophan was non-competitive with Ki at 2.75 x 10(-2) M. The effect of tryptophan on decarboxylation of dopa was small and it could not be expressed in terms of inhibition kinetics and inhibition constant. At physiological concentrations of aromatic amino acids in plasma, tryptophan does not seem to have remarkable effects on decarboxylation of phenylalanine, tyrosine, and dopa in the liver.

Amino Acids↗

PubMed1977

Decarboxylation-dependent transamination catalyzed by mammalian 3,4-dihydroxyphenylalanine decarboxylase.

In addition to the usual decarboxylation, pig kidney 3,4-dihydroxyphenylalanine (dopa) decarboxylase catalyzes a decarboxylation-dependent transamination which converts dopa into 3,4-dihydroxyphenylacetaldehyde and sinultaneously converts enzyme-bound pyridoxal-P into pyridoxamine-P. Similar reactions occur when this enzyme acts on m-tyrosine, alpha-methyldopa, and alpha-methyl-m-tyrosine. The transamination occurs in about 0.02% of decarboxylations of dopa and m-tyrosine and in about 2% of decarboxylations of alpha-methyldopa and alpha-methyl-m-tyrosine. The fraction of decarboxylations proceeding by the transamination pathway is independent of pH. This reaction appears to result from a divergence in the normal mechanism of decarboxylation; the quinoid intermediate which is formed by decarboxylation of the substrate-pyridoxal-P-Schiff base ordinarily protonates on the alpha carbon of the amino acid, but protonation occasionally occurs at the benzylic carbon of the coenzyme, and this latter route leads to transamination.

Animals↗

PubMed1986

Mechanism of the glycine cleavage reaction: retention of C-2 hydrogens of glycine on the intermediate attached to H-protein and evidence for the inability of serine hydroxymethyltransferase to catalyze the glycine decarboxylation.

Glycine is converted to carbon dioxide and an intermediate attached to a lipoic acid group on H-protein in the P-protein-catalyzed partial reaction of the glycine cleavage reaction [K. Fujiwara and Y. Motokawa (1983) J. Biol. Chem. 258, 8156-8162]. The results presented in this paper indicate that the decarboxylation is not accompanied by the removal of a C-2 hydrogen atom of glycine and instead both C-2 hydrogens are transferred with the alpha carbon atom to the intermediate formed during the decarboxylation of glycine. The purified chicken liver cytosolic and mitochondrial serine hydroxymethyltransferase preparations could not catalyze the decarboxylation of glycine in the presence of either lipoic acid or H-protein. The decarboxylation activity of the serine hydroxymethyltransferase preparation purified from bovine liver by the method similar to that of L. R. Zieske and L. Davis [(1983) J. Biol. Chem. 258, 10355-10359] was completely inhibited by the antibody to P-protein, while the antibody had no effect on the activity of the phenylserine cleavage. Conversely, D-serine inhibited the activity of phenylserine cleavage but the activity of the decarboxylation of glycine was not affected by D-serine. Finally, the two activities were separated by the chromatography on hydroxylapatite. The results clearly demonstrate that serine hydroxymethyltransferase per se cannot catalyze the decarboxylation of glycine.

Amino Acid Oxidoreductases↗

PubMed1990

Importance of spontaneous alpha-ketoacid decarboxylation in experiments involving peroxide.

The potential role of spontaneous alpha-ketoacid decarboxylation as a source of interference in experiments involving peroxide was investigated. The assay of pyruvate dehydrogenase activity in isolated renal mitochondria was employed as an example. Spontaneous peroxide-induced pyruvate decarboxylation competed significantly with enzymatic decarboxylation at peroxide concentrations greater than 50 microM. Corrected values for enzymatic decarboxylation could be obtained by subtracting spontaneous decarboxylation rates from rates obtained in the presence of mitochondria. At higher peroxide concentrations (greater than 200 microM), reaction product accumulates (acetoacetate) to levels which may have regulatory effects on mitochondrial metabolism. The divalent cations, Ca2+ and Mg2+, both accelerate spontaneous peroxide-induced pyruvate decarboxylation while other components of the assay medium had an inhibitory effect on the reaction. The results are discussed in relation to the currently accepted reaction mechanism. Investigators who perform experiments involving reactive oxygen species should be familiar with this often overlooked reaction.

Animals↗

PubMed1996

Arginine and ornithine decarboxylation in rodent brain: coincidental changes during development and after ischemia.

Agmatine, product of arginine decarboxylation, is known to occur mainly in bacteria and plants where it serves as a precursor for the synthesis of polyamines. Recently however, agmatine and arginine decarboxylation were detected in mammalian brain. Here we examined changes in rodent brain arginine decarboxylation during cerebellum development and after global forebrain ischemia and compared them to changes in ornithine decarboxylase, the enzyme catalyzing the first limiting step in polyamine synthesis. The findings suggest that (1) arginine decarboxylation is transiently increased during development and after ischemia in parallel to ornithine decarboxylase activity. (2) Arginine decarboxylation reaction is catalyzed by ornithine decarboxylase. (3) Decarboxylation of both ornithine and arginine becomes more pronounced in membrane fractions, rather than in the cytosol, during brain maturation. (4) During development, ornithine decarboxylase activity is reduced in the cytosol, but increased in the membrane fractions.

Animals↗