Human class III alcohol dehydrogenase/glutathione-dependent formaldehyde dehydrogenase.

The class III human liver alcohol dehydrogenase, identical to glutathione-dependent formaldehyde dehydrogenase, separates electrophoretically into a major anodic form (chi 1) of known structure, and at least one minor, also anodic but a slightly faster migrating form (chi 2). The primary structure of the minor form isolated by ion-exchange chromatography has now been determined. Results reveal an amino acid sequence identical to that of the major form, suggesting that the two derive from the same translation product, with the minor form modified chemically in a manner not detectable by sequence analysis. This pattern resembles that for the classical alcohol dehydrogenase (class I). Hence, the chi 1/chi 2 multiplicity does not add further primary forms to the complex alcohol dehydrogenase system but shows the presence of modified forms also in class III.