PURIFICATION, CHARACTERIZATION, AND PARTIAL SEQUENCE OF THE GLUTATHIONE-DEPENDENT FORMALDEHYDE DEHYDROGENASE FROM ESCHERICHIA-COLI - A CLASS-III ALCOHOL-DEHYDROGENASE

The glutathione-dependent formaldehyde dehydrogenase from Escherichia coli has been purified to homogeneity and characterized. It is a 83 000-kDa homodimer containing 4 g-atom of zinc per dimer with a specific activity of 60 units/mg toward S-(hydroxymethyl)glutathione and NAD+ as substrates. Its isoelectric point, 4.4, is consistent with both its amino acid composition and chromatographic behavior on DEAE HPLC. The N-terminus is unblocked, and 47 residues from the N-terminus were sequenced. A computer search of the Swiss-Prot protein sequence data bank shows that the N-terminal sequence, MKSRAAVAFAPGKPLEIVEIDVAPXKKGEVLIKVTHTGVcetDAFGL, is homologous with the mammalian class III alcohol dehydrogenases with 27 identities when compared to the human enzyme. Like the human, rat, and rabbit enzymes, it has high formaldehyde dehydrogenase activity in the presence of glutathione and catalyzes the oxidation of normal alcohols (ethanol, octanol, 12-hydroxydodecanoate) in a reaction that is not GSH-dependent. In addition, bemithiolacetals other than those formed from GSH, including omega-thiol fatty acids, also are substrates. The wide distribution and high degree of similarity of this enzyme to the plant and animal alcohol dehydrogenases suggest that the E. coli enzyme is closely related to the ancestor of the plant and animal dimeric zinc alcohol dehydrogenases.