FUNDAMENTAL MOLECULAR DIFFERENCES BETWEEN ALCOHOL-DEHYDROGENASE CLASSES

Citation
O. Danielsson et al., FUNDAMENTAL MOLECULAR DIFFERENCES BETWEEN ALCOHOL-DEHYDROGENASE CLASSES, Proceedings of the National Academy of Sciences of the United Statesof America, 91(11), 1994, pp. 4980-4984
Citations number
44
Categorie Soggetti
Multidisciplinary Sciences
ISSN journal
00278424
Volume
91
Issue
11
Year of publication
1994
Pages
4980 - 4984
Database
ISI
SICI code
0027-8424(1994)91:11<4980:FMDBAC>2.0.ZU;2-#
Abstract
Two types of alcohol dehydrogenase in separate protein families are th e ''medium-chain'' zinc enzymes (including the classical liver and yea st forms) and the ''short-chain'' enzymes (including the insect form). Although the medium-chain family has been characterized in prokaryote s and many eukaryotes (fungi, plants, cephalopods, and vertebrates), i nsects have seemed to possess only the short-chain enzyme. We have now also characterized a medium-chain alcohol dehydrogenase in Drosophila . The enzyme is identical to insect octanol dehydrogenase. It is a typ ical class III alcohol dehydrogenase, similar to the corresponding hum an form (70% residue identity), with mostly the same residues involved in substrate and coenzyme interactions. Changes that do occur are con servative, but Phe-51 is of functional interest in relation to decreas ed coenzyme binding and increased overall activity. Extra residues ver sus the human enzyme near position 250 affect the coenzyme-binding dom ain. Enzymatic properties are similar-i.e., very low activity toward e thanol (K-m beyond measurement) and high selectivity for formaldehyde/ glutathione (S-hydroxymethylglutathione; k(cat)/K-m = 160,000 min(-1). mM(-1)). Between the present class m and the ethanol-active class I en zymes, however, patterns of variability differ greatly, highlighting f undamentally separate molecular properties of these two alcohol dehydr ogenases, with class III resembling enzymes in general and class I sho wing high variation. The gene coding for the Drosophila class III enzy me produces an mRNA of about 1.36 kb that is present at all developmen tal stages of the fly, compatible with the constitutive nature of the vertebrate enzyme. Taken together, the results bridge a previously app arent gap in the distribution of medium-chain alcohol dehydrogenases a nd establish a strictly conserved class III enzyme, consistent with an important role for this enzyme in cellular metabolism.