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At least 163 records · Page 9Linked to original sources
PubMed1978

[Role of pyruvate kinase in non-specific changes of carbon photosynthetic metabolism, caused by the photophosphorylation inhibition].

The decrease in the level of NADP reduction in chloroplasts under injections of cofactors of pseudocyclic FMN photophosphorylation (vitamin K3 and methylviologen) into pea, tomato and cucumber leaves resulted in the decrease of 14CO2 autotrophic accumulation rate and in the change of distribution of assimilated carbon among the assimilation products. The inhibition of synthesis of labelled sugars and the increase of the content of 3-phosphoglyceric and glyceric acids in the labelled low molecular fraction were observed in all the experiments. Similar changes in the distribution of synthesized in Kalvin cycle labelled products, associated with the inhibition of its reduction unit, were observed under the effect of photophosphorylation uncoupling agents. However, the decrease of ATP/NADP ratio in chloroplasts resulted in the simultaneous increase of fixed 14CO2 incorporation into alanine. The role of pyruvate kinase in "alanine" effect, characteristic of non-specific changes of carbon photosynthetic metabolism, is discussed on the basis of the authors' previous data on the effect of phosphorylation on glycolysis reactions and on the basis of results of ADP introduction into leaf cuts.

Alanine↗
PubMed1976

The "phosphoryl-enzyme" from phosphoglycerate kinase.

The "phosphoryl-enzyme" prepared from phosphoglycerate kinase and adenosine 5'-triphosphate in the presence of an adenosine 5'-diphosphate trap is shown to contain stoichiometric amounts of 3-phosphoglycerate. This "phosphoryl-enzyme" is chemically competent, but is probably just a tight complex between 1,3-bisphosphoglycerate and the enzyme. The two partial exchange reactions (between adenosine 5'-diphosphate, and adenosine 5'-triphosphate, and between 3-phosphoglycerate and 1,3-bisphosphoglycerate) can both be observed, but their rates are very much slower than the rate of overall catalysis. No substrate analogue was found that accelerated the partial exchange reactions. Catalysis of each of the two exchange reactions and of the kinase reaction coincides after isoelectric focusing of purified enzyme, but the amount of cosubstrate necessary to cause the observed partial exchange rates is so small that these reactions may well be artifactual. The balance of evidence does not support a ping-pong pathway via phosphoryl-enzyme, and the reaction may be a sequential one in which the phosphoryl group is transferred between substrates in a ternary complex. The results point to the dangers in the interpretation of experiments where very small amounts of contaminating cosubstrate can lead to large kinetic effects, and to the possibility of mistaken deductions about the identity of reaction intermediates.

Adenosine Diphosphate↗
PubMed1997

Extraction of glyceric and glycolic acids from urine with tetrahydrofuran: utility in detection of primary hyperoxaluria.

Primary hyperoxaluria (PH) is an autosomal recessive metabolic abnormality characterized by excessive oxalate excretion leading to nephrocalcinosis and progressive renal dysfunction. Type I primary hyperoxaluria (PH I) results from a deficiency of alanine:glyoxylate aminotransferase, whereas type II disease has been traced to a deficiency of D-glycerate dehydrogenase. The two syndromes are often distinguished on the basis of organic acids that are coexcreted with oxalate: glycolate and L-glycerate in type I and type II disease, respectively. Routine organic acid analysis with diethyl ether extraction followed by gas chromatographic analysis failed to detect normal and increased concentrations of these diagnostic metabolites. Subsequent extraction of urine with tetrahydrofuran (THF), however, extracted 75% of added glycerate, 42% of added glycolate, and 75% of added ethylphosphonic acid (internal calibrator). THF extraction was analytically sensitive enough to allow determination of normal excretion of glycolate (14-72 micrograms/mg creatinine) and glycerate (0-5 years, 12-177 micrograms/mg creatinine and > 5 years, 19-115 micrograms/mg creatinine). Four of five patients with PH I and both patients with type II disease were correctly identified. Thus, THF extraction is a convenient adjunct to routine organic acid analysis and facilitates the detection of PH.

Adolescent↗
PubMed1999

Which organic acids does hemofiltrate contain in the presence of acute renal failure?

It is not generally possible to measure most organic acids in the serum of critically ill patients, due to rapid metabolism and methodological problems. Only the regular measurement of lactic acid and the arterial ketone body ratio (acetoacetate/beta-hydroxybutyrate, AKBR) have been introduced in clinical practice, but these parameters can represent only a part of the disturbed metabolism. In pediatric patients, a chromatographical urine analysis has been established for detection of inborn errors of metabolism, which allows the determination of more than 50 organic acids simultaneously (gas chromatographic (GC) analysis in combination with mass spectrometry (MS)]. In continuous treatment of acute renal failure, hemofiltrate is always available, but it contains only low protein concentrations and after the filtration process, metabolism is rapidly stopped. The sieving coefficient of lactic acid is nearly one in hemofiltration. The aim of our study was to compare results of the regular and CG/MS methods in blood and hemofiltrate for lactic acid, and to find other organic acids of possible clinical importance. We investigated serum (lactic acid) and hemofiltrate of 40 critically ill patitens, similar to the urine analysis method for infants. All patients suffered from acute renal failure and were treated by continuous veno-venous hemofiltration (CVVH). The conditions of treatment were standardized (spontaneous ultrafiltration in the first hour), and the material (blood/hemofiltrate) was taken one hour after the beginning of extracorporeal circulation. Statistical methods included correlation analysis, nonparametric ANOVA with Wilcoxon scores (ranks of data), and stepwise discriminant analysis. Regular and GC/MS methods in hemofiltrate showed a good correlation for lactic acid. The best correlation with lactic acid was found for 4-hydroxy-phenyllactic acid (n=20, r=0.866), 2-hydroxy-valeric acid (n=22, r=0.7491) and 2-hydroxybutyric acid (n=32, r=0.5148). Age, sex, diagnosis, and APACHE II score play a subordinate role, but the presence of glyceric and citric acid possibly have prognostic importance [nonparimetric ANOVA with Wilcoxon scores (ranks of data)], as does the combination of 3-hydroxypropionic acid, glyceric acid, and threonic-acid-4-lacton (stepwise discriminant analysis). It can be concluded that in acute renal failure, the measurement of lactic acid and AKBR can reflect only a small part of disturbed metabolism. Hemofiltrate can be a useful medium in describing metabolic processes in critically ill patients with acute renal failure. Some inherited metabolic diseases in infants (phenylketonuria, maple syrup disease) and ketoacidosis show similar metabolic modifications.

APACHE↗
PubMed1989

Biochemical contribution to diagnosis and study of a new case of D-glyceric acidemia/aciduria.

During organic acid screening by gas chromatography/mass spectrometry, we detected a large peak corresponding to glyceric acid in a patient's urine sample. The D(+) configuration was demonstrated by a polarimetric method and by enzymatic stereospecificity of D-glycerate dehydrogenase (EC 1.1.1.29). We biochemically investigated this fifth reported case of D-glyceric acidemia. In our patient, loading tests with L-serine and fructose led to an increase of D-glyceric acid in both plasma and urine. Determination of other metabolites involved in D-glycerate metabolism revealed no abnormality in any sample examined. After comparing all our results with those of the preceding observations described in the literature, we suggest a possible enzymatic defect located on one of the metabolic pathways shared by fructose and L-serine, possibly at the level of hepatic D-glycerate kinase (EC 2.7.1.31). Nevertheless, a primary defect of L-serine catabolism cannot be entirely excluded.

Chemical Phenomena↗
PubMed2006

Sugar fragmentation in the maillard reaction cascade: formation of short-chain carboxylic acids by a new oxidative alpha-dicarbonyl cleavage pathway.

The formation of short-chain carboxylic acids was studied in Maillard model systems (90 degrees C, pH 6-10) with emphasis on the role of oxygen and water. The total amount of acetic acid formed did not depend on the reaction atmosphere. In the presence of labeled dioxygen or water (18O2, H2 17O), labeled oxygen was partially incorporated into acetic acid. Thermal treatment of 1-deoxy-d-erythro-2,3-hexodiulose (1) and 3-deoxy-d-erythro-hexos-2-ulose in the presence of 17O-enriched water under alkaline conditions led to acetic and formic acid, respectively, as indicated by 17O NMR spectroscopy. The suggested mechanism involves an oxidative alpha-dicarbonyl cleavage leading to an intermediary mixed acid anhydride that releases the acids, e.g., acetic and erythronic acid, from 1. Similarly, glyceric and lactic acids were formed from 1-deoxy-3,4-hexodiuloses, corroborated by complementary analytical techniques. This paper provides for the first time evidence for the direct formation of acids from C6-alpha-dicarbonyls by an oxidative mechanism and incorporation of a 17OH group into the carboxylic moiety. The experimental data obtained support the coexistence of at least two newly described reaction mechanisms leading to carboxylic acids, i.e., (i) a hydrolytic beta-dicarbonyl cleavage as a major pathway and (ii) an alternative minor pathway via oxidative alpha-dicarbonyl cleavage induced by oxidizing species.

Acetic Acid↗
PubMed1998

[Steroids and lipids from Spirodela polyrrhiza].

Two steroids and two lipids were isolated from the ethanolic extract of Spirodela polyrrhiza. Their structures were identified by spectral analysis and chemical evidence, which were identified as stigmasterol, monopalmitic glycerate, daucosterol and palmitic acid. Monopalmitic glycerate was discovered from this plant for the first time.

Chromatography, Thin Layer↗
PubMed1982

Structural factors influencing the ability of compounds to inhibit hydroxyapatite formation.

For a compound to inhibit potently the transformation of amorphous calcium phosphate into hydroxyapatite, it is suggested that the minimum structural requirement is a phosphate group and, at some other position, either another phosphate group preferably or a carboxylic moiety. Primary amino groups abolish inhibitor potential. Inhibitor potency is modified by various secondary factors, including the number and proximity of active groups, their stereochemistry, steric factors, the lability of the molecule, and in special instances its lipophilicity. Parameters used to monitor the transformation indicate that inhibitors can be grouped into two classes, and it is suggested that this is because one class acts as a hydroxyapatite crystal growth inhibitor. The close proximity of two phosphate groups or of a phosphate and multiple carboxylic groups is proposed to determine in part whether or not a compound acts as a crystal growth inhibitor. Further, bulky side groups render a molecule inactive as a crystal growth poison, although it will still inhibit by other mechanisms.

Adenosine Triphosphate↗