Subunits horse liver alcohol dehydrogenase

In the case of horse liver alcohol dehydrogenase, a homodimeric enzyme, Subramanian et al.(202) used the relative phosphorescence of tyrosine and tryptophan to examine the effects of various ternary complexes known to selectively quench the fluorescence of the tryptophans of each subunit. One proposed quenching mechanism is the formation of a ground-state tyrosinate in a ternary complex at neutral pH.(201) This tyrosinate, by being a resonance... 

Horse liver alcohol dehydrogenase has a molecular weight of 80 000 and is made up of two subunits, each containing two zinc atoms. The subunits are not active in the monomeric form. 

A crystal structure of a ternary complex of horse liver alcohol dehydrogenase with NADH and the inhibitor, dimethyl sulfoxide, first at 4.5 A resolution1365 and a further refinement to 2.9 A resolution,1366 has been published by Eklund et al. The gross structure of the ternary complex is similar to that of the free enzyme structure. Each subunit is divided into a coenzyme-binding domain and a catalytic domain. The subunits are joined together near the... 

Fig. 25. Chain trace of one subunit of horse liver alcohol dehydrogenase. Stereo drawing from the work of Branden and colleagues [117], The catalytic zinc atom is central, the structural zinc atom is at the bottom right.

The substrate binding pocket of horse liver alcohol dehydrogenase comprises residues from both subunits (Fig. 26B) [123]. The active site is shown in Fig. 27, with NAD(H) bound, and p-bromobenzyl alcohol bound in a non-productive binding mode. The hydrophobic residues (from both subunits) that line the substrate binding... 

Fig. 26. (A) Schematic diagram of one subunit of horse liver alcohol dehydrogenase. Znl is the active-site zinc. Designed by B. Furugren, from the work of Branden and colleagues [55], (B) Schematic diagram of a section through the horse liver alcohol dehydrogenase dimer. The catalytic zinc atoms are shown, with the inhibitory substrate analogue DMSO and coenzyme molecules indicated. The dimer has two active sites, each composed of parts of both subunits. From the work of Branden and colleagues [123].

Horse liver alcohol dehydrogenase was first crystallized by Bonnichsen and Wasson in 1948 (34) An acidic minor component was isolated by Dalziel (35), and different forms were later shown to exist (36,37). Neither of these studies revealed the true isozyme pattern of horse liver alcohol dehydrogenase, and an increasing number of different molecular forms have since been characterized. The multiplicity is a result of the synthesis of different types of subunits as well as of the occurrence of secondary modified forms. 

Horse liver alcohol dehydrogenase is an NAD -dependent enzyme that catalyzes the oxidation of various primary and secondary alcohols to their corresponding aldehydes. The active enzyme is a dimer composed of two identical subunits. Each... 

The second zinc ion present in each horse liver alcohol dehydrogenase subunit is four-coordinate (47), and the four ligands are arranged in a tetrahedral array about the metal ion. However, all four ligands are derived from amino acid side chains (cysteinyl sulfhydryls) contributed by the protein. In neither case is the... 

The horse liver alcohol dehydrogenase, crystallized by my collaborators Bonnichsen and Wassen in 1948, has been subject to much work the last 20 years, both in my lab and others. Its amino acid sequence (374 residues per subunit = molecule) was cleared up by my young collaborator Hans Jornvall working with I. J. Harris in Cambridge from 1967 and then with us in Stockholm. Alcohol dehydrogenases from other sources were also studied in our and many other peoples laboratories. It is at present one of the most intensively studied enzymes in the world. 

Fig. 1. Horse liver alcohol dehydrogenase. Peptide chain folding in the two subunits. Fig. 2. Coenzyme and substrate pocket in the ADH molecule (explanation see text).

When designing models of coenzymes it is important to examine the structure of the corresponding enzymes. The three-dimensional structure of horse liver alcohol dehydrogenase has been resolved at 0.24 nm resolution by the group of C. I. Branden from Uppsala (280) and has been correlated to a number of physical and chemical studies in solution. The active enzyme has a molecular weight of 80,000 and is a dimer of two identical subunits. 

Yeast and mammalian alcohol dehydrogenases differ in substrate specificity and catalytic activity. The yeast enzyme is more specific for acetaldehyde and ethanol, but mammalian enzymes have a broad substrate specificity, and even with primary alcohols maximum activity is not observed with ethanol. Because of the large amount of alcohol dehydrogenase present in human liver and its role in alcohol metabolism in man, human liver alcohol dehydrogenase is of particular interest. It was first purified by Wartburg et and crystallized by Mourad and Woronick. Human liver alcohol dehydrogenase is a dimer with subunit structures analogous to those of horse liver, and each subunit probably contains two zinc atoms. Several different types of human ADH have been isolated. with minor variations in amino acid... 

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