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Query: EC:1.1.1.37 (malate dehydrogenase)
 4,591 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The association reactions of NADH and NAD+ with dimeric pig heart supernatant malate dehydrogenase (s-MDH) have been measured at pH 6 and 8 by calorimetric and fluorescence methods, and the thermodynamic parameters describing these reactions have been evaluated. Coenzyme binding is associated with the uptake of 0.55 mol of H+/mol of NADH at pH 8 and 0.19 mol of H+ at pH 6. No significant effect of NAD+ binding on proton binding was observed. Increase in ionic strength strongly affects the free energies of binding of NAD+ and NADH. No cooperativity was observed in the enthalpy or free energy changes for binding of NAD+ or NADH. The differences in free energy of binding of NAD+ and NADH and the effect of pH on binding of NADH are entropy based. These effects are interpreted as reflecting a small number of interactions within the active site that are predominantly ionic.
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PMID:Binding of reduced and oxidized nicotinamide adenine dinucleotide to pig heart supernatant malate dehydrogenase. 22 14

The changes induced by phenobarbital in cerebral enzymatic activities of the Krebs' cycle (citrate synthase, malate dehydrogenase) and electron transfer chain (total NADH-cytochrome c reductase and cytochrome oxidase) were studied. In addition, the activity of lactate dehydrogenase of acetylcholine esterase and of glutamate dehydrogenase was also studied. These enzymatic activities were evaluated in the homogenate in toto and in a crude mitochondrial fraction from rat brain. The modifications in some of these activities indicate that several new metabolic situations occur in brain tissue after phenobarbital treatment.
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PMID:Effect of phenobarbital on cerebral energy state and metabolism. Enzymatic activities. 23 Jun 18

A proposed mechanism [Clin. Chem. 19, 668 (1973)] for the inverse relationship between guanidinoacetate (I) and guanidinosuccinate (II) in human urine is explored. The mechanism proposes that canavaninosuccinate (III) may be reduced to form homoserine and II or, alternatively, that the III may be acted upon by a lyase to form canavanine and fumarate. The canavanine would then proceed to transamidinate to glycine to form I. This study demonstrates for the first time that lyase activity for converting III to canavanine and fumarate exists in human liver and kidney extracts. Transamidination from canavanine to glycine to form I is also readily accomplished with human tissue. Reductive cleavage of III to II and homoserine has been demonstrated before [Clin. Chem. 15, 397 (1969)]. The optimum pH for the lyase reaction is 6.5, for the reductive cleavage it is 8.7. In following the course of the lyase reaction, we developed a technique whereby the fumarate formed was hydrated with fumarase (EC 4.2.1.2) and then dehydrogenated with malate dehydrogenase (EC 1.1.1.37). The changes in absorbance of NADH formed in the reaction were then measured and used to determine the amount of fumarate formed, as a measure of lyase activity. Canavanino-succinate lyase activity follows pseudo-first-order reaction kinetics. The Michaelis constant of this lyase was 6.16 X 10-4 mol/liter, for argininosuccinate lyase 9.74 X 10-4 mol/liter. These data suggest that the binding affinity for III to the enzyme is greater than that for argininosuccinate. Glycine added to the reaction acts as an activator, probably because it removes the canavanine from the reaction mixture. On the other hand, arginine acts as an inhibitor of III-lyase. Other substances tested, such as canavanine, fumarate, and argininosuccinate had no effect on the reaction kinetics.
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PMID:Evidence supporting a proposed mechanism explaining the inverse relationship between guanidinoacetate and guanidinosuccinate in human urine. 23 5

A proposed mechanism [Clin. Chem. 19, 668 (1973)] for the inverse relationship beteen guanidinoacetate (I) and guanidinosuccinate (II) in human urine is explored. The mechanism proposes that canavaninosuccinate (III) may be reduced to form homoserine and II or, alternatively, that the III may be acted upon by a lyase to form canavine and fumarate. The canavanine would the proceed to transamidinate to glycine to form I. This study demonstrates for the first time that layse activity for converting III to canavanine and fumarate exists in human liver and kidney extracts. Transamidination from canavine to glycine to form I is also readily accomplised with human tissue. Reductive cleavage of III to II and homoserine has been demonstrated before [Clin. Chem. 15, 397 (1969)]. The optimum pH for the lyase reaction is 6.5, for the reductive cleavage it is 8.7. In follwing the course of the lyase reaction, we developed a technique whereby the fumarate formed was hydrated with fumarase (EC 4.2.1.2) and then dehydrogenated with malate dehydrogenase (EC. 1.1.1.37). The changes in absorbance of NADH formed in the reaction were then measured and used to determine the amount of fumarate formed, as a measure of lyase activity. Canavanino-succinate lyase activity follows pseudo-first-order reaction kinetics. The Michaelis constant of this lyase was 6.16 X 10-4 mol/liter, for argininosuccinate lyase 9.74 X 10.4 mol/liter. These data suggest that the binding afficinity for III to the enzyme is greater than that for argininosuccinate. Glycine added to the reaction acts as an activator, probably because is removes the canavanine from the reaction mixture. On the otherhand, arginine acts as an inhibitor of III-lyase. Other substances tested, such as canavaine, fumarate, and arginissuccinate had no effect on the reaction kinetics.
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PMID:Evidence supporting a proposed mechanism explaning the inverse relationship between guanidinoacetate and guanidinosuccinate in human urine. 23 6

Kinetic studies on the pig heart cytoplasmic malate dehydrogenase have been performed over a wide range of conditions using the full time course of the reaction and computer simulation to obtain the kinetic parameters. The maximum velocity and Michaelis constants for the oxidation of reduced coenzyme have been determined as a fundtion of pH in 0.05 M phosphate buffer at 15 degrees. At pH 7.5 and at low substrate concentrations, the kinetic data are consistent with a sequential addition of substrates, coenzyme binding first, and involving the formation of at least one ternary complex. No oxalacetate binding to the enzyme was observed. The rate constants for the dissociation of coenzyme from the enzyme-coenzyme complex are small enough to define the maximum velocity in either direction of the reaction. These data, plus data using deuterated reduced coenzyme, indicate that the chemical transformation step is not rate determining. It is also shown that DPNH binding can be tight enough to practically exclude the possibility of obtaining initial velocities when measuring the reduction of DPN. Kinetic abnormalities do appear at higher substrate or product concentrations, but these do not appear to be related to the formation of inactive abortice, complexes.
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PMID:Kinetic studies on pig heart cytoplasmic malate dehydrogenase. 23 57

A multienzyme complex from Euglena, molecular weight about 360,000, containing phosphoenolpyruvate carboxylase, malate dehydrogenase, and acetyl-coenzyme A carboxylase has been dissociated into active constituent enzymes. The respective molecular weights are 183,000, 67,000, and 127,000. The malate dehydrogenase contained in the complex is electrophoretically distinct from other malate dehydrogenase isozymes found in Euglena. The K-m for HCO3minus of the free and complexed acetyl-CoA carboxylase is 4.2-5.4 mM, and the substrate dependency for acetyl-CoA describes a sigmoidal relationship. The HCO3minus K-m for the free phosphoenolpyruvate carboxylase is 7.3-5.4 mM while that for the same enzyme contained in the complex is 0.7-1.3 mM. Both the free and complexed forms ofphosphoenolpyruvate carboxylase have a K-m for phosphoenolpyruvate of 0.9-1.7 mM. The latter enzyme in both the complex and free forms is stimulated by NADH, acetyl-CoA, and ATP. In the free phosphoenolpyruvate carboxylase, the stimulation passes through a maximum depending on effector concentration. The effect of NADH is to increase V-max while K-m values remain unmodified.
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PMID:Dissociation and characterization of enzymes from a multienzyme complex involved in CO2 fixation. 23 77

Bovine mitochondrial malate dehydrogenase (EC 1.1.1.37) was inactivated by the specific modifications of a single histidine residue upon reaction with iodoacetamide. NADH protected against this loss of activity and reaction with the histidine residue, suggesting that the histidine is at the NADH binding site. N-Ethylmaleimide also modified the enzyme by reacting with 1 sulfhydryl residue. The reaction rate with N-ethylmaleimide was increased by decreasing the pH from neutrality or by the addition of urea. NADH protected against the modification of the sulfhydryl group under all the conditions tested, again suggesting active site specificity for this inactivation. This enzyme has a subunit weight of 33,000 and is a dimer. The native malate dehydrogenase will bind only 1 mol of NADH and it is thus assumed that there is only a single active site per dimer.
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PMID:Chemical modification of bovine heart mitochondrial malate dehydrogenase. Selective modification of cysteine and histidine. 23 21

Low concentrations (less than 0.2% w/v) of phenoxyethanol stimulated both the rate of respiration and total oxygen uptakes of Escherichia coli NCTC 5933 suspensions with glucose and other substrates, whilst higher concentrations (0.2--0.6% w/v) although still below those showing significant bactericidal activity, produced progressive levels of inhibition. The degree of respiratory inhibition varied with different substrates in the order malate less than succinate less than pyruvate less than or equal to glucose less than lactate, and suggested appreciable inhibition at a point after malate in the tricarboxylic acid cycle. This suggestion was supported by the use of tetrazolium salts as alternative electron acceptors, and by cytochrome difference spectra, which together implicated malate dehydrogenase as the most likely site of action. Isolated dehydrogenase enzymes of the tricarboxylic acid cycle in cell-free preparations were unaffected by high concentrations of phenoxyethanol (0.8% w/v) with the exception of malate dehydrogenase which was inhibited in extracts to extents similar to those of malate oxidation by intact bacteria. Lineweaver-Burke plots for malate dehydrogenase activity in the presence of phenoxyethanol suggested a competitive inhibition of the oxaloacetic acid-limited reaction and a non-competitive inhibition of the NADH-limited reaction. Accordingly, Ki values were found to be low when the rate of reaction was limited by oxaloacetic acid concentration yet relatively high when NADH was rate limiting.
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PMID:Inhibition of some respiration and dehydrogenase enzyme systems in Escherichia coli NCTC 5933 by phenoxyethanol. 36 31

For human mammary and ovarian carcinomas and transplantation tumours of rats clear hints found for an enzymatic-lytic effects of infiltrating tumour cells as a premise of the invasive tumour growth. In contrast in malignant melanomas there is no functional sign for a specific enzymatic-lytic effect of the living tumour cells to the surrounding tissue. In the mamma carinomas and ovarian carcinomas infiltratively growing tumour districts were characterized by an increased activity of the NADH-D, LDH, G-6-P-DH, IDH, MDH, SPase, UE, LAP and beta-GD. The transplantation tumours showed a high number of tumour cells with a high leucine amino-peptidase- and beta-glucuronidase-activity in a middle zone that was localized under the tumour edge district. The increased activity of the LAP and beta-GD found in the infiltration zone of the tumours is considered as an demonstration of a strong proteolytic activity of the tumour cells. The findings are discussed in the aspect of the invasive tumour growth.
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PMID:[Histochemical and ultrastructural investigations on invasive growth of tumour. I. Enzyme-histochemical investigations (author's transl)]. 40 21

1. In a group of 23 obese women the relations between some indicators of thyroid function (thyroxine-binding globuline--T4BG, triiodothyronine-binding globuline--T3BG, Achilles tendon reflex--ART) on the one hand and activities of enzymes of the energy metabolism (hexokinase--HK, triose phosphate dehydrogenase--TPDH, lactate dehydrogenase--LDH, glycerol-3-phosphate dehydrogenase--GPDH, citrate synthease--CS, malate dehydrogenase--MDH, hydroxyacyl--COA dehydrogenase) in the quadriceps femoris muscle on the other hand were investigated. 2. Correlations were found between T4BG and TPDH, LDH and GPDH activities, between T3BG and TPDH and GPDH activities and between the value of the Achilles tendon reflex and TPDH activity. Functionally these enzymes activities are associated with glycolysis and hydrogen transport from cytoplasmatic NADH2. No correlations were found between enzymes of the aerobic metabolism incl. enzymes of fatty acid oxidation and indicators of thyroid function. 3. The results indicate a relationship between thyroid function and enzymes involved in glycolysis and hydrogen transport from cytoplasmatic NADH2. They do not suggest, however, the unequivocal conclusion that in obese women with reduced thyroid function there is a generally reduced energy supplying metabolism in skeletal muscle.
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PMID:Obesity and thyroid function. 3. Relationship between some indicators of thyroid function and the energy metabolism of striated muscle in obese women. 41 51


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