SEQUENTIAL OXIDATION OF ALCOHOLS BY ALCOHOL DEHYDROGENASE

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The alcohol dehydrogenases, ADHs, have been pivotal to the developent of enzymology and have widespread applications. Liver ADHs have been the primary focus of investigations and show broad substrate specificity, oxidizing alcohols from methanol to steroids. They also have the ability to oxidize aldehydes to acids. This activity is not widely recognized, although there have been sporadic reports in the literature of related phenomena. The prevailing view, however, is that the reported kinetic values for both aldehyde oxidation and aldehyde dismutation preclude the physiological relevance of this reaction. The core of this proposal is that horse liver alcohol dehydrogenase, HL- ADH, is not just able to oxidize aldehydes as an intriguing, albeit nonphysiological side reaction; but when assayed under conditions that do not obscure this activity it is fully competent to catalyze the oxidation of aliphatic aldehydes to acids with catalytic efficiencies comparable to and even much greater than its catalysis of alcohol oxidation. Our focus in the past year has been on conducting detailed kinetic studies to determine the kinetic values for the reaction and fitting them to an overall kinetic scheme. We are also developing the methodology to allow determining the ability of other alcohol dehydrogenases to conduct the facile oxidation of aldehydes to acids. Our current focus has been on kinetic studies. As we obtain more information on the ability of other alcohol dehydrogenases to oxidize aldehydes, we will need to begin to compare their structures and also with ADHs that do not readily oxidize aldehydes. At that time we anticipate a major effort focused on the use of the Computer Graphics Laboratory to interpret the structure/activity relations and interpretation of sequence analyses of related proteins. At present we are still in the data gathering stage but we are starting a project with Dr. P. Babbitt on structural alignments and graphics will become an essentia part of the project.