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PubMed1991

Nonhomogeneous labeling of liver mitochondrial acetyl-CoA.

The specific activity of carbons 1 and 2 of plasma acetoacetate has been used as a measure of the specific activity of liver mitochondrial acetyl-CoA in tracer studies. To test whether or not acetoacetate actually reflects acetyl-CoA, livers were perfused with a mixture of substrates that are converted to mitochondrial acetyl-CoA: 1 mM lactate, 0.2 mM pyruvate, 0.2 mM acetate, and, where indicated, 0.2 mM octanoate or 0.2 mM alpha-ketoisocaproate. In each experiment, one of these substrates was 13C-labeled. Labeling of mitochondrial acetyl-CoA was assessed by three methods: (i) molar percent enrichment of total tissue acetyl-CoA; (ii) molar percent enrichment of carbons 4 and 5 of tissue citrate, the precursor of which is acetyl-CoA; and (iii) molar percent enrichment of carbons 1 and 2 of perfusate ketone bodies. Nonhomogeneous labeling of liver mitochondrial acetyl-CoA occurred under most conditions, i.e. the enrichments of carbons 4 and 5 of citrate were different from enrichments of carbons 1 and 2 of ketone bodies. Thus, based upon our results obtained in perfused livers, we question the validity of measuring the labeling of carbons 1 and 2 of acetoacetate as a noninvasive probe of liver mitochondrial acetyl-CoA.

Acetates↗
PubMed1985

Head-space gas-chromatographic determination of 3-hydroxybutyrate in plasma after enzymic reactions, and the relationship among the three ketone bodies.

In this sensitive, reproducible method for determination of D-3-hydroxybutyrate (3-OHB) in plasma, it is converted to acetone by use of 3-hydroxybutyrate dehydrogenase (EC 1.1.1.30)/lactate dehydrogenase (EC 1.1.1.27) coupled with acetoacetate decarboxylase (EC 4.1.1.4). The resulting acetone is detected by head-space gas chromatography. The lowest concentration of 3-OHB detectable in plasma was 2 mumol/L. The calibration curve showed a linear relationship for 3-OHB concentration from 0 to 5 mmol/L (r = 0.999). Analytical recovery of 3-OHB (50 mumol/L) was 97.9 (SD 3.8)%. The method was developed for determination of the three ketone bodies in plasma. The ratio of acetone to acetoacetate was not significantly different (p greater than 0.2) between normals (n = 31) and diabetics (n = 86). In normal subjects, the ratio of 3-OHB to acetoacetate was 1.20 (SD 0.44). In diabetic patients, the ratio correlated with the logarithm of the total ketone body concentration (r = 0.828).

3-Hydroxybutyric Acid↗
PubMed1979

Significance of blood ketone body ratio as an indicator of hepatic cellular energy status in jaundiced rabbits.

Changes in the free NAD+/NADH ratio and the energy charge (ATP + 1/2 ADP/ATP + ADP + AMP) of the liver were compared with the ratio of acetoacetate to beta-hydroxybutyrate of arterial blood in rabbits subjected to ligation of the common bile duct. Both the acetoacetate/beta-hydroxybutyrate ratio of the liver, which reflects mitochondrial free NAD+/NADH ratio, and the heptic energy charge decreased in accordance with the decrease of mitochondrial phosphorylative activity after the ligation. The decrease in the acetoacetate/beta-hydroxybutyrate ratio of the liver was attributed to a restricted mitochondrial reoxidation of NADH due to an inhibition of oxidative phosphorylation. Moreover, changes in the ratio of acetoacetate to beta-hydroxybutyrate in arterial blood were positively correlated with those of the liver (r = 0.695, P less than 0.01) and the hepatic energy charge (r = 0.844, P less than 0.01). It is suggested that the ratio of acetoacetate to beta-hydroxybutyrate in blood can reflect the energy charge of the liver in jaundiced rabbits.

Acetoacetates↗
PubMed1982

Sampling of arterialized heated-hand venous blood as a noninvasive technique for the study of ketone body kinetics in man.

To determine if sampling of arterialized-hand venous (HV) blood is a suitable alternative for arterial (A) blood to study ketone body metabolism, concentrations of unlabeled and labeled ketone bodies were measured during continuous infusion of 3-14C-acetoacetate in simultaneously drawn samples from A and HV blood in normal subjects. The mean difference of acetoacetate between A and HV blood was in the basal state 1.5% and that of beta-hydroxybutyrate 6% (n.s.). Similarly, the 14C-content of ketone bodies and their calculated rates of production of metabolic clearance were not significantly different between A and HV blood. Following induction of ketosis by acetoacetate loading infusions, the difference of concentrations and 14C-content of total ketone bodies between HV and A blood remained insignificant (average 3%), and ketone body kinetics calculated from A and HV blood were similar. Furthermore, concentrations of glucose, lactate and pCO2 did nit differ significantly between the two sampling sites. In contrast, concentrations of ketone bodies, glucose and pO2 were significantly lower, and the metabolic clearance rate of ketone bodies and pCO2 higher in antecubital venous blood compared to heated-hand venous blood. Thus, the similarity of heated-hand venous and arterial blood suggests that the noninvasive technique is suited for kinetic analyses using tracer methods and for arteriovenous balance studies of ketone bodies.

Acetoacetates↗
PubMed1977

New approach to determination of total ketone bodies in serum.

We describe a one-step assay for total ketone bodies in serum. D-BETA-Hydroxybutyrate is enzymatically oxidized by NAD+ to acetoacetate. This thermodynamically unfavorable reaction is driven to completion by coupling it with the enzymatic reduction of pyruvate by NADH. The acetoacetate so formed, as well as the pre-existing acetoacetate, is quantitatively decarboxylated to acetone in a gas chromatograph and measured directly. Thus by a single measurement for acetone, all three ketone bodies are simultaneously determined. In light of the ubiquity of situations associated with augmented ketone body production, the clinical implications of this approach are extensive.

Acetoacetates↗
PubMed1996

Use of corticosteroids alone or combined with glucose to treat ketosis in dairy cows.

OBJECTIVE: To compare relative efficacy of dexamethasone and flumethasone alone or in combination with rapid IV infusion of glucose for treatment of ketosis in cattle. DESIGN: Clinical trial. ANIMALS: 127 cows with urine acetoacetate concentration > or = 60 mg/dl. PROCEDURE: Cows were treated with 500 ml of 50% glucose solution. IV, and 40 mg of dexamethasone, IM (group 1), 40 mg of dexamethasone, IM (group 2), 5 mg of flumethasone (group 3), or 500 ml of 50% glucose solution, IV, and 5 mg of flumethasone (group 4). Treatment success was defined as recovery after a single treatment without relapse during the same lactation. Uterine disease (retained placenta or metritis), parity, and pretreatment plasma glucose, serum beta-hydroxybutyric acid, and urine acetoacetate concentrations were evaluated as possible confounding factors affecting recovery. RESULTS: Only uterine disease was found to have a significant effect on recovery. Treatments 1 and 4 were significantly more efficacious than was treatment 2, but efficacy of treatment 2 was not significantly different from that of treatment 3. Regardless of treatment, cows with uterine disease were less likely to have a successful outcome than were cows without uterine disease. In all treatment groups, plasma glucose concentration increased and serum beta-hydroxybutyric acid and urine acetoacetate concentrations decreased following treatment. CLINICAL IMPLICATIONS: In this study, treatment of ketosis in dairy cattle with a corticosteriod alone was less efficacious than treatment with glucose and a corticosteroid.

3-Hydroxybutyric Acid↗
PubMedDate not supplied

[Plasma progesterone and ovarian findings related to plasma glucose and acetoacetat in the postpartum period in the cow (author's transl)].

Ovarian function and carbohydrate status were examined in 286 dairy cows. The cows, which were at various stages of the postpartum period, had their ovaries examined by one rectal palpation. Simultaneously with the clinical examination, one blood sample was taken for determination of progesterone, glucose and acetoacetate. In the period before 24 days post partum cows not having a corpus luteum had somewhat lower plasma glucose than cows having a corpus luteum (P less than 0.05). Cows not having a corpus luteum after 40 days showed a tendency to lower plasma glucose and higher plasma acetoacetate than cows having corpus luteum (P less than 0.05). Ovarian activity, expressed through frequency of high progesterone values (greater than or equal to 2 ng/ml), increased markedly after 40 days post partum, while the lowest glucose means and highest frequencies of acetoacetate greater than or equal to 2.5 mg/100 ml occurred before 30 days post partum. It is concluded that longitudinal studies post partum will be required to clarify the possible effect of hypoglycemia on the ovarian function.

Acetoacetates↗
PubMed1983

Effects of hyperthyroidism on stimulation of [1-14C]oleate oxidation to 14CO2 in isolated hepatocytes from fed rats by the catecholamines, vasopressin, and angiotensin II.

Possible effects of adrenaline, noradrenaline, vasopressin, and angiotensin II to increase 14CO2 production from [1-14C]oleate were examined in hepatocytes from fed L-triiodothyronine (T3)-treated or control rats. Rates of 14CO2 production were decreased and rates of ketogenesis increased in hepatocytes from T3-treated rats. These changes were accompanied by a marked shift of the 3-hydroxybutyrate:acetoacetate concentration ratio towards acetoacetate. Rates of glucose and lactate release were decreased. Whereas the Ca2+-mobilizing hormones increased 14CO2 production from [1-14C]oleate by 64-84% with hepatocytes from control rats, they increased 14CO2 production from [1-14C]oleate by on 24-32% with hepatocytes from T3-treated rats. The magnitude of the response to the Ca2+-mobilizing hormones in hepatocytes from T3-treated rats was increased by the addition of 3-mercaptopicolinate, an inhibitor of phosphoenolpyruvate carboxykinase, to the incubation medium (increases of 52-88%). In the presence of 3-mercaptopicolinate, the 3-hydroxybutyrate:acetoacetate concentration ratio in hepatocytes from fed, T3-treated rats was similar to that in hepatocytes from control rats in the absence of 3-mercaptopicolinate. The results demonstrate that hyperthyroidism per se does not lead to a loss of sensitivity, in terms of oleate oxidation, either to the catecholamines or to vasopressin and angiotensin II. The impaired ability of hepatocytes from T3-treated rats to respond to these hormones is a consequence of decreased net glycolytic flux or a more oxidized mitochondrial redox state.

Angiotensin II↗
PubMed1989

Relationships between the NAD(P) redox state, fatty acid oxidation, and inner membrane permeability in rat liver mitochondria.

Dysfunction of mitochondria after oxidation of endogenous NAD(P)H, especially after calcium accumulation, has been abundantly reported, but the causes of membrane perturbations did not receive a full explanation. In light of several additional observations reported in this study, we propose a general scheme which shows the sequential processes that are likely involved in the appearance of calcium-induced membrane leakiness. Addition of acetoacetate, oxaloacetate, or ketomalonate to rotenone-treated mitochondria led to a massive oxidation of both NADH and NADPH. Under these conditions, stimulation of fatty acid oxidation could be observed. This process was shown to be accompanied by a reduction of intramitochondrial NADP+. The reduction of NADP+ was inhibited by uncouplers, electron transfer inhibitors and N,N'-dicyclohexylcarbodiimide. It was thus probably catalyzed by the mitochondrial transhydrogenase. Oxidation of pyridine nucleotides in the presence of acetoacetate induced (i) a slight decrease in the number of sulfhydryl groups reactive with N-ethylmaleimide (but no change in the amount of intramitochondrial reduced glutathione) and (ii) modifications of the kinetics and the orientation of the ADP/ATP carrier. In the presence of calcium ions, acetoacetate-stimulated fatty acid oxidation promoted an extensive swelling of mitochondria. Uptake of calcium ions into the matrix was a critical factor for triggering the swelling. Thiols, if they were added at a sufficiently high concentration, suppressed the swelling. Also ligands of the ADP/ATP carrier which stabilized the m-state conformation of the protein, exerted an efficient protective action. Three essential interacting factors emerge from this study: (i) The crucial role of the ADP/ATP carrier orientation in promoting the calcium-induced membrane destabilization. More precisely, it has been shown that the ADP/ATP carrier adopts the c-state conformation (i.e., nucleotide binding site facing the cytoplasm) during fatty acid oxidation. (ii) The modification of a very small number of sulfhydryl groups of mitochondrial protein. These groups are probably in an oxidized state when the level of reduced pyridine nucleotides is low. (iii) The prevailing role of the transhydrogenase, the function of which is also intimately associated with fatty acid oxidation. After energization, transhydrogenase can hinder thiol oxidation and therefore partially protect the membrane structure.

Adenosine Diphosphate↗
PubMed1996

Mechanism-based inactivation of gamma-aminobutyric acid aminotransferase by 3-amino-4-fluorobutanoic acid.

The mechanism of inactivation of the pyridoxal 5'-phosphate (PLP)-dependent enzyme gamma-aminobutyric acid (GABA) aminotransferase by 3-amino-4-fluorobutanoic acid (2) has been investigated. As in the case of the homologue, 4-amino-5-fluoropentanoic acid (1), 2 equiv of radiolabeled inactivator become covalently attached to the enzyme, and no transamination, as determined by the lack of conversion of [1-14C] alpha-ketoglutarate into [1-14C] glutamate during inactivation, was observed. In the case of 1, the conclusion was that inactivation was completely the result of modification of the coenzyme and that there was no metabolic turnover; every enzyme molecule catalysed the conversion of one molecule of inactivator to the activated species, which inactivated the enzyme by an enamine mechanism. With 2, however, 6.7 +/- 0.7 equiv of fluoride ions were released during inactivation, and it took 7.6 +/- 0.7 inactivator molecules to inactivate each enzyme dimer. Since no transamination was occurring, another metabolic event besides inactivation must result from the PLP form of the enzyme. Inactivation of GABA amino-transferase with [1,2-14C]-2 produced [14C] acetoacetic acid (about 5.5 equiv) as the metabolite. The 1.93 +/- 0.25 equiv of radioactivity covalently bound to the enzyme after inactivation with [1,2-14C]-2 and gel filtration were completely released by base treatment. HPLC analysis showed that three radioactive compounds, identified as 2, the product of reaction of PLP with acetone (3), and the product of reaction of PLP with acetoacetate (4), were detected. The release of 3 and 4 and the prevention of release of radioactivity by treatment with sodium borohydride are consistent with the formation of covalent intermediates that have beta-carbonyl-like character, such as 6 and/or 7 (Scheme 2). Inactivation of [3H] PLP-reconstituted GABA aminotransferase with 2 followed by gel filtration then base denaturation released all of the radioactivity as a mixture of PLP, 3, and 4. Inactivation with [1,2-14C]-2 resulted in the release of 1.37 equiv of 14CO2, which was shown to be the result of decarboxylation of the acetoacetate/4 after release from the enzyme. These results are not consistent with a Michael addition mechanism (Scheme 3), but are consistent with inactivation by an enamine mechanism; release of the enamine five out of seven turnovers accounts for the formation of acetoacetate as the metabolite. To account for the detection of PLP and 2 after denaturation, it is suggested that a nonproductive formation of the Schiff base of PLP with 2 occurs in the second subunit of the enzyme; this complex is released and hydrolysed to PLP and 2 upon base denaturation.

4-Aminobutyrate Transaminase↗
PubMed2004

Evaluation of diabetes-related short-chain organic acids in rat plasma by capillary electrophoresis.

A capillary zone electrophoresis method was optimised to analyse low-molecular-mass organic acids for the purpose of monitoring diabetes in rat plasma. The method included acetoacetic, 2-hydroxybutyric, lactic and uric acids. A variation in the background electrolyte allowed us to measure pyruvic acid in the same sample. Conditions have been optimised for measuring a large number of plasma samples corresponding to control and diabetic rats. Samples were mixed with acetonitrile (1:1, v/v) to precipitate proteins, centrifuged, diluted and injected. Tropic acid was chosen as an adequate internal standard. Separation was developed with reversed voltage by using a column cartridge pre-treated with polyacrylamide. Two electrophoretic buffers were employed: 0.150 M H3PO4 made up pH 6.20 with NaOH and 0.3 mM CaCl2 for acetoacetic, hydroxybutyric, lactic and uric acids, and 200 mM phosphate-10 mM acetate pH 4.0 for pyruvic acid, both with direct detection at 200 nm. The method was validated for linearity, accuracy and precision and the limits of quantification were calculated. The method was successfully applied to analyse these organic acids in control and diabetic animals. Acetoacetic and hydroxybutyric acids were clearly increased in diabetic rats, meanwhile no statistically significant difference has been found with the other acids.

Animals↗
PubMed1989

Plasma carnitine concentration and lipid metabolism in infants receiving parenteral nutrition.

The relationships among plasma total carnitine concentration, postnatal age, and fatty acid metabolism were evaluated in 57 infants receiving parenteral nutrition. Concentrations of plasma carnitine, triglycerides, free fatty acids, acetoacetate, and beta-hydroxybutyrate were determined before and at 2 and 4 hours from the beginning of a standardized 2-hour lipid infusion. Plasma carnitine concentrations declined with increasing postnatal age. There were no significant differences in gestational age or triglyceride concentrations between infants less than or equal to 4 weeks of age and those greater than 4 weeks of age, whereas free fatty acid concentrations were lower and acetoacetate and beta-hydroxybutyrate concentrations were higher in the younger infants. Infants less than or equal to 4 weeks of age were further grouped according to plasma carnitine concentration greater than 13 nmol/ml (group 1) and less than or equal to 13 nmol/ml (group 2) and were then compared with infants greater than 4 weeks of age (group 3). There were no significant differences in triglyceride concentrations among the three groups; free fatty acids, acetoacetate, and beta-hydroxybutyrate concentrations for group 2 patients were similar to those of group 1 patients or fell between values for group 1 and group 3 patients. These results demonstrate decreasing plasma carnitine concentrations and possibly for more than 4 weeks.

Aging↗
PubMed1999

Rational medium design for Bordetella pertussis: basic metabolism.

In current Bordetella pertussis media ammonium accumulates because of an imbalance in the nitrogen:carbon ratio of the substrates used, which is one of the factors limiting cell density in fed-batch cultures. The aim of this study was to map B. pertussis catabolic and anabolic capabilities, in order to design a medium that avoids ammonium accumulation, while substrates are metabolised completely. Besides the known dysfunctional glycolysis, B. pertussis also possessed a partially dysfunctional citric-acid cycle. Although ammonium accumulation was avoided by adding various carbon sources to medium with glutamate, nuclear magnetic resonance (NMR) showed excretion of acetate, acetoacetate and beta-hydroxy-butyrate, thereby reducing the biomass yield. Acetoacetate and beta-hydroxy-butyrate were also formed in Verwey, B2 and modified Stainer-Scholte medium. Electron microscopy in combination with NMR showed that cells early on in these cultures contained poly-hydroxy-butyrate (PHB) globules, which disappeared later during the culture, coinciding with the appearance of beta-hydroxy-butyrate and/or acetoacetate. No globules nor metabolite excretion was detected when lactate in combination with glutamate were used as substrates. Thus, metabolite excretion and ammonium accumulation were avoided, while the yield of 8.8 g C-mol-1 compared favourably with literature values, averaging 6.5 g C-mol-1. Optimisation of this medium for pertussis toxin production will be reported in a separate article.

Bordetella pertussis↗
PubMed1983

3-hydroxy-3-methylglutaryl-CoA lyase: catalysis of acetyl coenzyme A enolization.

3-Hydroxy-3-methylglutaryl-CoA lyase, which performs the cleavage of 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) to acetoacetate and acetyl-CoA by a Claisen-type reaction, also catalyzes enolization of acetyl-CoA. The rate of detritiation of methyl-labeled acetyl-CoA is proportional to enzyme concentration and is diminished by an antiserum that also inhibits the cleavage reaction. The tritium-exchange reaction requires both divalent cation and acetoacetate. An analogue of HMG-CoA, 3-hydroxyglutaryl-CoA, was prepared by reaction of acetonedicarboxylic anhydride with CoASH and reduction of the ketoacyl-CoA product with cyanohydridoborate. While 3-hydroxyglutaryl-CoA does not appear to be a substrate for HMG-CoA lyase, it competitively inhibits both the cleavage reaction (Ki = 50 microM) and the tritium exchange from acetyl-CoA (Ki = 95 microM). Agreement between the Ki values measured for cleavage and for tritium exchange supports the hypothesis that the slow tritium exchange is a lyase-dependent reaction. Initial attempts to demonstrate complete reversibility of the cleavage reaction have not been successful. However, the data suggest that the cleavage of HMG-CoA is at least partially reversible and indicate that enolization of acetyl-CoA may be dependent upon a conformational change of HMG-CoA lyase, induced by binding of acetoacetate, in a manner analogous to the keto acid dependent tritium exchange catalyzed by malate synthase and citrate synthase.

Acetyl Coenzyme A↗
PubMed1995

Synthesis, structure, and pharmacological evaluation of the stereoisomers of furnidipine.

The synthesis and pharmacological activities of the four stereoisomers of methyl tetrahydrofuran-2-ylmethyl 2,6-dimethyl-4-(2'-nitrophenyl)-1,4-dihydropyridine-3,5- dicarboxylate(furnidipine) are reported. The four isomers were synthesized by a modified Hantzsch synthesis by reaction of (-)- or (+)-tetrahydrofuran-2-ylmethyl 3-aminocrotonate and methyl 2-[(2'-nitrophenyl)methylene]acetoacetate or, alternatively, by reaction of (-)- or (+)-tetrahydrofuran-2-ylmethyl 2-[(2'-nitrophenyl)methylene]acetoacetate and methyl 3-aminocrotonate. The 1:1 diastereomeric mixtures thus obtained were separated by chromatography, using poly(D-phenylglycine) as the chiral stationary phase. The enantiomeric purity of the stereoisomers was determined by a high-performance liquid chromatography-chiral stationary phase technique (HPLC-CSP). Attempts to obtain crystals of a single stereoisomer failed in different solvents, while methanol crystallization of the product obtained from (+/-)-tetrahydrofuran-2-ylmethyl 2-[(2'-nitrophenyl)methylene]acetoacetate and methyl 3-aminocrotonate yielded good-quality crystals of the most insoluble racemate which proved to be a mixture of the (SS)/(RR) enantiomers by X-ray crystallography. Conformational analysis of the stereoisomers, assuming rotation of the aryl substituent and ester groups, shows small energy differences (about 4 kcal.mol-1) between the most and the least favorable conformations. Binding studies were performed using [3H]isradipine as a reference ligand. The results showed stereospecificity of the furnidipine isomers in brain, ileum, and cardiac tissues, the (SS)- and (SR)-isomers clearly being more potent than their (RR)- and (RS)-enantiomers. The (SS)- and (SR)-isomers were also more selective on cerebral tissue when compared with ileal and cardiac preparations.

Animals↗
PubMed1997

A Reexamination of the Mechanism of the Biginelli Dihydropyrimidine Synthesis. Support for an N-Acyliminium Ion Intermediate(1).

The mechansim of the three-component Biginelli dihydropyrimidine synthesis was reinvestigated using (1)H and (13)C NMR spectroscopy. Condensation of benzaldehyde, ethyl acetoacetate, and urea (or N-methylurea) in CD(3)OH according to the procedure described by Biginelli produced the expected 6-methyl-2-oxo-4-phenyl-1,2,3,4-tetrahydropyrimidine-5-carboxylates. According to NMR measurements, there is no evidence that the first step in the Biginelli reaction is an acid-catalyzed aldol reaction of ethyl acetoacetate and benzaldehyde leading to a carbenium ion intermediate, as has been suggested previously. In contrast, all experimental evidence points to a mechanism involving an N-acyliminium ion as the key intermediate, formed by acid-catalyzed condensation of benzaldehyde and urea (or N-methylurea). Interception of this iminium ion by ethyl acetoacetate produces open-chain ureides which subsequently cyclize to the Biginelli dihydropyrimidines.

Journal Article↗
PubMed1976

Effect of phenylalanine metabolites on the activities of enzymes of ketone-body utilization in brain of suckling rats.

1. The effects of phenylalanine and its metabolites (phenylacetate, phenethylamine, phenyl-lactate, o-hydroxyphenylacetate and phenylpyruvate) on the activity of 3-hydroxybutyrate dehydrogenase (EC 1.1.1.30) 3-oxo acid CoA-transferase (EC 2.8.3.5) and acetoacetyl-CoA thiolase (EC 2.3.1.9) in brain of suckling rats were investigated. 2. The 3-hydroxybutyrate dehydrogenase from the brain of suckling rats had a Km for 3-hydroxybutyrate of 1.2 mM. Phenylpyruvate, phenylacetate and o-hydroxyphenylacetate inhibited the enzyme activity with Ki values of 0.5, 1.3 and 4.7 mM respectively. 3. The suckling-rat brain 3-oxo acid CoA-transferase activity had a Km for acetoacetate of 0.665 mM and for succinyl (3-carboxypropionyl)-CoA of 0.038 mM. The enzyme was inhibited with respect to acetoacetate by phenylpyruvate (Ki equals 1.3 mM) and o-hydroxyphenylacetate (Ki equals 4.5 mM). The reaction in the direction of acetoacetate was also inhibited by phenylpyruvate (Ki equals 1.6 mM) and o-hydroxyphenylacetate (Ki equals 4.5 mM). 4. Phenylpyruvate inhibited with respect to acetoacetyl-CoA both the mitochondrial (Ki equals 3.2 mM) and cytoplasmic (Ki equals 5.2 mM) acetoacetyl-CoA thiolase activities. 5. The results suggest that inhibition of 3-hydroxybutyrate dehydrogenase and 3-oxo acid CoA-transferase activities may impair ketone-body utilization and hence lipid synthesis in the developing brain. This suggestion is discussed with reference to the pathogenesis of mental retardation in phenylketonuria.

Acetyl-CoA C-Acetyltransferase↗
PubMed1985

Fuel utilization in colonocytes of the rat.

In incubated colonocytes isolated from rat colons, the rates of utilization O2, glucose or glutamine were linear with respect to time for over 30 min, and the concentrations of adenine nucleotides plus the ATP/ADP or ATP/AMP concentration ratios remained approximately constant for 30 min. Glutamine, n-butyrate or ketone bodies were the only substrates that caused increases in O2 consumption by isolated incubated colonocytes. The maximum activity of hexokinase in colonic mucosa is similar to that of 6-phosphofructokinase. Starvation of the donor animal decreased the activities of hexokinase and 6-phosphofructokinase, whereas it increased those of glucose-6-phosphatase and fructose-bisphosphatase. Isolated incubated colonocytes utilized glucose at about 6.8 mumol/min per g dry wt., with lactate accounting for 83% of glucose removed. These rates were not affected by the addition of glutamine, acetoacetate or n-butyrate, and starvation of the donor animal. Isolated incubated colonocytes utilized glutamine at about 5.5 mumol/min per g dry wt., which is about 21% of the maximum activity of glutaminase. The major end-products of glutamine metabolism were glutamate, aspartate, alanine and ammonia. Starvation of the donor animal decreased the rate of glutamine utilization by colonocytes, which is accompanied by a decrease in glutamate formation and in the maximum activity of glutaminase. Isolated incubated colonocytes utilized acetoacetate at about 3.5 mumol/min per g dry wt. This rate was not markedly affected by addition of glucose or by starvation of the donor animal. When colonocytes were incubated with n-butyrate, both acetoacetate and 3-hydroxybutyrate were formed, with the latter accounting for only about 19% of total ketones produced.

Adenine Nucleotides↗