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Query: EC:1.1.1.49 (glucose-6-phosphate dehydrogenase)
 7,794 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Homogeneous glycogen phosphorylase from human leukocytes has been obtained. A one-step bioluminescent procedure for the enzyme activity assay has been developed. This method is based on a continuous recording of the product of the glycogen phosphorylase-catalyzed reaction using a coimmobilized multienzyme system (phosphoglucomutase, glucose-6-phosphate dehydrogenase, NADH:FMN oxidoreductase and bacterial luciferase). The method sensitivity is 10 times as high compared to earlier described methods. The Km values for glycogen (0.2 mg/ml) and phosphate (3.9 mM) at pH 7.9 were determined. AMP was shown to be the enzyme effector.
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PMID:[Glycogen phosphorylase from human leukocytes. Isolation and kinetic properties]. 211 14

Topical application on rat oral mucosa of the chemical 4-nitroquinoline 1-oxide (4NQO) has been shown to produce squamous cell carcinomas on the posterior tongue and/or the posterior hard palate. 4NQO is broken down in vivo by a diaphorase, 4NQO reductase (E.C.1.6.99.2), to produce an active molecule believed to be responsible for carcinogenesis. It has been shown that there are higher concentrations of 4NQO reductase in oesophageal mucosa compared with elsewhere in the gastrointestinal tract. The purpose of these experiments was to compare the distribution of certain diaphorases in the oral mucosa. Samples of rat tongue and cheek epithelia were homogenized, then ultracentrifuged to provide mixed cytosol and microsome fractions from the epithelial cells. A spectrophotometer was used to measure the variation in absorbance at 340 nm of NADH consumed by reduction of 4NQO by enzymes present in the tissue extracts. A histochemical technique was used to compare the activity of NADH diaphorase, NADP diaphorase and glucose-6-phosphate dehydrogenase at different sites of the oral mucosa. Statistical analysis showed that there were significant (P less than 0.01) differences between the activities of all three enzymes at different sites of the oral mucosa. In each case, a higher activity was found at the sites of high incidence of squamous cell carcinoma. A lower activity was found at sites where carcinomas did not occur.
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PMID:A relationship found between intra-oral sites of 4NQO reductase activity and chemical carcinogenesis. 211 96

Postural muscles have many type I myofibers, which reacted strongly for acid-stable myosin ATPase and were unreactive for alkali-stable myosin ATPase (Ariano et al., J. Histochem. Cytochem., 21:51-55, 1973; Armstrong et al., Am. J. Anat., 163:87-98, 1982; Smith et al., J. Neurophysiol., 40:503-513, 1977). House shrews (Suncus murinus) keep abducting their limbs in locomotion and hardly lift their trunk off the ground. The limb muscles of Suncus were examined by histochemical methods to determine whether the locomotory and postural behavior is related to the proportion of type I myofibers. The observation of whole cross sections from the triceps surae, flexor digitorum superficialis, quadriceps femoris, and caudally situated muscles in the thigh showed that all myofibers of these muscles were unreactive for acid-stable myosin ATPase and strongly reactive for alkali-stable myosin ATPase: Those were classified as type II myofibers. Type II myofibers showed a weak (type IIB), moderate (type IIAB), or strong (type IIA) reaction for NADH tetrazolium reductase. Part of type IIA myofibers reacted weakly to moderately for menadione-linked glycerol-3-phosphate dehydrogenase (m-GPD), which predominated in the soleus muscle. Type IIAB, type IIB, and the remainder of type IIA myofibers reacted strongly for m-GPD. The limb muscles contained subtypes of type II myofibers but no type I myofibers. In Suncus murinus, type I myofibers specialized for a postural maintenance may not be required because all myofibers function exclusively for propulsion.
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PMID:Composition of myofiber types in limb muscles of the house shrew (Suncus murinus): lack of type I myofibers. 214 5

Homogenates of human and pig brain in 10 mM Tris-HCl, pH 8.0 were centrifuged at 25,400 x g for 1 h. The supernatants were electrophoresed in polyacrylamide gels were stained for glucose-6-phosphate dehydrogenase (EC 1.1.1.49) activity. Five distinct bands were visible. Isozymes corresponding to two of those bands were purified from human and pig brain. The isozymes were electrophoretically homogeneous. The native proteins, Mr, 220,000, dissociated in sodium dodecyl sulphate-polyacrylamide gels into a 57,000 Mr subunit. Therefore, the native isozymes are tetramers. None of the isozymes required additional metal ions for activity. At 1 mM concentration Mg2+ and Ca2+, independently or together, activated the isozymes 1.5-fold. The isozymes were NADP(+)-specific. Kmapp values of the G6PD isozymes were similar for NADP+ (6-8 microM), but different for G6P (56-180 microM). The specific activities of the isozymes varied from 50 to 210 units per mg of protein. All isozymes were inhibited by NADPH. The inhibition was competitive with respect to NADP+ and non-competitive with respect to G6P. NADH did not affect any of the isozymes. ATP inhibited the isozymes competitively with respect to G6P and non-competitively with respect to NADP+. Palmitoyl-CoA dissociated the active tetramers into enzymatically inactive dimeric forms. This treatment also abolished the 6-phosphogluconate activity of the isozyme II from both sources. High performance liquid chromatography peptide maps of the tryptic digest and amino acid analyses of the isozymes showed extensive homologies between the corresponding isozymes from the two species. Interestingly, only the isozyme II in human and pig brain was active with 6-phosphogluconate as a substrate (Kmapp = 864 and 279 microM). The specific activities of the isozyme II with 6-phosphogluconate (14 and 48 unit per mg of protein for human and pig brain isozyme II, respectively) was four times less than those with G6P. It is therefore suggested that isozyme II is a bifunctional enzyme.
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PMID:Characterization of glucose-6-phosphate dehydrogenase isozymes from human and pig brain. 227 Jan 45

Experiments are presented that confirm earlier predictions that the mode of supply of reactants to a nonlinear (bio)chemical reaction determines or controls concentrations at steady states far from equilibrium. The oxidation of nicotinamide adenine dinucleotide (NADH) catalyzed by the enzyme horseradish peroxidase with continuous input of oxygen was studied; NAD+ is continuously recycled to NADH through a glucose-6-phosphate dehydrogenase system. A comparison of steady-state concentrations is made with an oscillatory oxygen input and a constant input at the same average oxygen input for both modes. By varying the frequency and amplitude of the perturbation (O2 influx), the following may be changed: the average concentration of NADH; the Gibbs free energy difference delta G of the reactants and products at steady state; the average rate of the reaction; the phase relation between the oscillatory rate and delta G; and the dissipation. These results confirm the possibility of an "alternating current chemistry," of control and optimization of thermodynamic efficiency and dissipation by means of external variation of constraints in classes of nonlinear reactions and biological pumps, and of improvements of the yield in such reactions (heterogeneous catalysis, for example).
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PMID:Changes in mean concentration, phase shifts, and dissipation in a forced oscillatory reaction. 229 1

Stereospecificities are reported for seven dehydrogenases from Acholeplasma laidlawii, an organism from an evolutionarily distinct branch of life which has not previously been studied from a stereochemical point of view. Three of the activities examined (alcohol dehydrogenase, lactate dehydrogenase, and alanine dehydrogenase) catalyze the transfer of the pro-R (A) hydrogen from NADH. Four other activities (3-hydroxy-3-methylglutaryl-CoA reductase, glyceraldehyde-3-phosphate dehydrogenase, glucose-6-phosphate dehydrogenase, and NADH oxidase) catalyze the transfer of the pro-S (B) hydrogen from NAD(P)H. The stereospecificity of hydroxymethylglutaryl-CoA reductase is notable because it is the opposite of that of hydroxymethylglutaryl-CoA reductases from yeast and rat. These data are used to derive the simplest historical model capable of explaining available experimental facts.
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PMID:The stereospecificities of seven dehydrogenases from Acholeplasma laidlawii. The simplest historical model that explains dehydrogenase stereospecificity. 236 93

Chemiluminometric methods are described for the automated flow injection analysis of NADPH and NADH using an immobilized enzyme column reactor and serum magnesium. This application is for the clinical analysis of NADPH and NADH. The reactor for NADPH and NADH contains immobilized L-glutamate dehydrogenase and L-glutamate oxidase, and that for serum magnesium immobilized hexokinase, glucose-6-phosphate dehydrogenase, L-glutamate dehydrogenase and L-glutamate oxidase. When the sample is introduced into the four-enzyme bioreactor, hydrogen peroxide is produced in proportion to the concentration of serum magnesium by the successive reactions. A co-immobilized hexokinase/glucose-6-phosphate dehydrogenase/glutamate dehydrogenase column reactor gave better efficiency compared with an enzyme column which was prepared by packing co-immobilized hexokinase/glucose-6-phosphate dehydrogenase and immobilized glutamate dehydrogenase to make two layers. Magnesium in serum was determined with 1 microL of the sample without carry-over and for an assay time of approximately 15 s. The present method is sensitive (detection limit 0.1 nmol) because Mg2+ is recycled in a column, and gives perfect linearity of the data up to 3.0 mmol/L with satisfactory precision, reproducibility, and accurate reaction recoveries.
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PMID:A chemiluminometric method for NADPH and NADH using a two-enzyme bioreactor and its application to the determination of magnesium in serum. 238 94

Two fast-twitch fiber types are histochemically identified in the primary flight muscles of Artibeus jamaicensis. These are classified as type IIa and IIb according to an acid-preincubation staining protocol for myosin ATPase. All fibers in the bat flight muscles exhibit relatively intense staining properties for NADH-TR, suggesting a high oxidative capacity. The glycolytic potential of all fibers is rather low, as assessed by stains for alpha-GPD. This two-type histochemical profile appears to parallel biphasic electromyographic patterns observed in these muscles and leads us to propose that flight muscle histochemistry and activation are mediated by a "two-gear" neuromuscular control system. In contrast, earlier studies on Tadarida brasiliensis demonstrate the existence of a "one-gear" neuromuscular control system, exemplified by the presence of one fiber type. These observations are discussed with respect to the natural history and flight styles of several species.
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PMID:Histochemistry of flight muscles in the Jamaican fruit bat, Artibeus jamaicensis: implications for motor control. 245 76

DHEA, a steroid precursor of androgens and estrogens has also an inhibitory effect on several enzymes, namely on 11 beta-hydroxylase, NADH oxidase and glucose 6-phosphate dehydrogenase. The latter is the rate limiting enzyme of the pentose phosphate cycle. This metabolic pathway provides the cells with extramitochondrial NADPH and pentose phosphates. NADPH is used for the synthesis of fatty acids and steroids. Together with ribose 5-phosphate, NADPH (as coenzyme of folate reductases) is required for the synthesis of nucleic acids. A deficient production of DHEA has been found to be responsible for several diseases obesity, diabetes type 2, hypertension, arteriosclerosis and hyperuricemia as well as malignant growth (low DHEA syndrome). DHEA administration favourably modified several of these metabolic disorders. These studies were started in our laboratory in 1962 and stopped in 1976 because we were short of DHEA. At that time the response to our results was rather theoretical, but the last years a new wave of interest in DHEA called for two consecutive symposia, where important findings were presented (Paris in January and Jena in April 1989). It is a damage that this new trend, started in our laboratory, could not be pursued up to now without interruption.
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PMID:[Dehydroepiandrosterone. Renaissance after 13 years]. 252 67

The mechanism of acetaldehyde-mediated GOT inhibition was studied in human red cells. In the GOT assay mix, acetaldehyde competitively inhibits activation of apoGOT by pyridoxal phosphate and pyridoxamine phosphate. However, Ki values are 100-1000 times greater than Km values for these B6 vitamers. Moreover, incubation of undiluted lysates with acetaldehyde at 37 degrees inhibits GOT activity without increasing apoGOT levels and without altering affinity of apoGOT for either B6 coenzyme. In undiluted lysates, inhibition is not prevented by disulfiram. However, incubation at 4 degrees prevents both acetaldehyde metabolism and GOT inhibition while preincubation with NaF prevents GOT inhibition without affecting acetaldehyde disappearance. The effect of NaF is completely reversed by pyruvate but only partially reversed by NADH. Glyceraldehyde 3-phosphate, the only glycolytic intermediate which directly inhibits GOT, does not reverse the NaF effect. Thus, inhibition of GOT by acetaldehyde (a) requires nonoxidative metabolism of acetaldehyde and (b) is not mediated either by glycolytic substrates or by impaired binding of B6 vitamers to the GOT apoenzyme. Since NaF had no effect on a lysate deficient in glucose 6-phosphate dehydrogenase, the hexose monophosphate shunt may play a role in acetaldehyde-mediated GOT inhibition.
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PMID:Studies on the mechanism of acetaldehyde-mediated inhibition of aspartate aminotransferase (GOT) in human erythrocytes. 259 35


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