Structural Studies of Human‐Liver Alcohol‐Dehydrogenase Isoenzymes

1 Alcohol dehydrogenase isoenzymes BE were isolated from human livers of both “normal” and “atypical” phenotypes [1]. Their pH‐rate profiles, their behaviour on CM‐cellulose and the number of hybrids formed with horse subunit A show that the “atypical” isoenzymes contain subunits B1 and B2 the “normal” one only subunit B1. These results indicate that most “atypical” individuals genetically represent heterozygotes. 2 A high degree of homology between horse subunit A and human subunits B is found. However, the human isoenzymes have a molecular weight of 87000 and contain about 410 amino acid residues, 6 tyrosines and 3 tryptophans per subunit. 3 The sequence of one tryptic peptide from subunit B1 is Phe‐Ala‐Lys and is altered to Phe‐Pro‐Lys in the subunit B2. This substituted residue is located in a region which corresponds to the coenzyme‐binding site of the horse enzyme.