Dehydrogenases studies

Inhibitors of lactic dehydrogenase have been reported in commercial preparations of NAD+ and NADH (B4, M6, S28). The concentration of inhibitory substances varied from lot to lot. In a serum lactic dehydrogenase study with NAD+ from 8 sources, activities were found to vary from 145 to 75 units (B4). Inhibitors of lactic dehydrogenase activity have also been observed in dialyzates in uremic patients (W8) and in human urine (G8). The purity of available substrate can also effect enzyme activity. Schwartz and Bodansky observed that, in 6 batches of fructose 6-phosphate, all weighed to a 0.5 mM concentration, the actual concentration varied from 0.13 mAf to 0.55 mM (S14). 

Nearly all NAD+-dependent dehydrogenases studied follow an ordered bisubstrate mechanism. In this mechanism, the oxidation of a substrate proceeds in a sequential manner first, NAD+ binds in the active site of the dehydrogenase then the substrate binds next a hydride equivalent is transferred in a chemical step from the bound substrate to the bound NAD+, hence, oxidising the substrate and reducing the NAD+ to NADH the oxidised substrate is then released from the active site and is finally followed by the NADH. 

D9. Dovrat, A., and Gershon, D Rat lens superoxide dismutase and glucose-6-phosphate dehydrogenase Studies on the catalytic activity and fate of enzyme antigen as a function of age. Exp. Eye Res. 33, 651-661 (1981). 

There is no uniformity in the effect of pH on the dissociation constants of the NAD compounds. The pronounced decrease of Xe.nad for liver alcohol dehydrogenase from pH 6.0 to pH 10.0 was attributed to ionization of a water molecule coordinated to the active center zinc atom and Coulombic interaction with the nicotinamide N-1 (64)- The absence of a similar pH effect with the other dehydrogenases studied so far is understandable on this basis. Structural studies of the compounds of liver alcohol dehydrogenase with ADPR and 1 10-phenanthroline, competitive... 

Rat Kidney -h-Amino Add Oxidase Dehydrogenase). Studies by Krebs clearly indicated that different systems existed in animal tissues for the oxidation of n- and L-amino acids. However, while considerable success has been achieved in the purification of mammahan n-amino acid... 

Ryde U (1996) The coordination of the catalytic zinc ion in alcohol dehydrogenase studied by combined quantum-chemical and molecular mechanics calculations. J Comput Aided Mol Des 10 153-164... 

A. Amino Acid Analysis and Sequence. B. Immuno-diffusion. C. Density (iradient Sedimentation. D. Tritium-Labeling. E. Neutron Activation of Phosphorus. F. Histo-chemical Methods and Starch Gel Electrophoresis for Dehydrogenase Studies. G. Nuclear Magnetic Resonance and Electron Spin Resonance. H. Infra-red Measuremctits in Aqueous Media. I. Optical Rotatory Dispersion. 

The Protein Data Bank PDB ID 1A71 Colby T D Bahnson B J Chin J K Klinman J P Goldstein B M Active Site Modifications m a Double Mutant of Liver Alcohol Dehydrogenase Structural Studies of Two Enzyme Ligand Com plexes To be published... 

Alcohol dehydrogenase-catalyzed reduction of ketones is a convenient method for the production of chiral alcohols. HLAD, the most thoroughly studied enzyme, has a broad substrate specificity and accommodates a variety of substrates (Table 11). It efficiendy reduces all simple four- to nine-membered cycHc ketones and also symmetrical and racemic cis- and trans-decalindiones (167). Asymmetric reduction of aUphatic acycHc ketones (C-4—C-10) (103,104) can be efficiendy achieved by alcohol dehydrogenase isolated from Thermoanaerohium hrockii (TBADH) (168). The enzyme is remarkably stable at temperatures up to 85°C and exhibits high tolerance toward organic solvents. Alcohol dehydrogenases from horse Hver and T. hrockii... 

A free energy study of malate dehydrogenase [29] using semiempirical QM-MM methods has also been reported, and that shidy also attributes many of the benefits to simulation of enzyme reactions found in the BPTP shidy. 

Uncovering of the three dimentional structure of catalytic groups at the active site of an enzyme allows to theorize the catalytic mechanism, and the theory accelerates the designing of model systems. Examples of such enzymes are zinc ion containing carboxypeptidase A 1-5) and carbonic anhydrase6-11. There are many other zinc enzymes with a variety of catalytic functions. For example, alcohol dehydrogenase is also a zinc enzyme and the subject of intensive model studies. However, the topics of this review will be confined to the model studies of the former hydrolytic metallo-enzymes. 

As another example, studies with deuterium-labeled substrates have shown that the reaction of ethanol with the coenzyme NAD+ catalyzed by yeast alcohol dehydrogenase occurs with exclusive removal of the pro-R hydrogen from ethanol and with addition only to the Re face of NAD+. 

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