ALCOHOL DEHYDROGENASE: MORE STRUCTURES - IMPLICATIONS TO SPECIFICITY AND FUNCTION. Ramaswamy S., El Ahmed M., Jörvall H., Plapp B.V., and Eklund H. Department of Molecular Biology, Biomedical Center, Uppsala Sweden; Department of Medical Biochemistry and Biophysics, Karolinksa Institute, Stockholm; Sweden and Department of Biochemistry, University of Iowa, Iowa City, USA.

Electron transfer pathway and the specificity of alcohol dehydrogenase (ADH) have been investigated by determining a number of structures. We have determined the structure of ADH from cod fish and several substrate and product analogue complexes of ADH from horse liver to reasonably high resolutions.

The cod fish class I ADH is closer in sequence and hence in phylogeny to the class III ADH's, which are considered the primordial ADH's. The structure was determined by molecular replacement and refined to 2.1 Ang resolution. The structure is very similar in the core regions and most of the changes are in the loops. The changes in the loops alone seem to govern the type of substrate that binds and the activity of these enzymes. The absence of the His H-bonded to the ribose suggests that this residue is probably not important for the activity of this enzyme unlike the mammalian enzymes.

Ternary complexes of Alcohol dehydrogenase with bromobenzyl alcohol, penta fluoro benzyl alcohol, hepta fluoro butanol, n-formyl piperidine, and cyclo hexyl formamide reveal the flexible nature of substrate binding to the large pocket in this enzyme. However, the pentafluoro benzyl alcohol is bound in a such a way that its modelled pro-R hydrogen is positioned towards the C4 of the NAD., poised for this proton to be transferred, suggesting that this is probably the form just before the proton is transferred. The structure of this enzyme with a potential drug, 3-butyl tmso in its two isoforms has also been determined. The results of all these studies will be presented.