Identification of a segment containing a reactive cysteine residue in human liver cytoplasmic aldehyde dehydrogenase (isoenzyme E1)

A single cysteine residue is selectively alkylated by iodoacetamide in cytoplasmic human liver aldehyde dehydrogenase (isoenzyme E1). The amino acid sequence of a 35-residue fragment containing this residue is determined, showing two additional cysteine residues and also three histidine residues. The alkylation is selective for Cys-30 of this fragment, with only little alkylation even at an adjacent residue, Cys-29. The region examined is likely to be of significance in the reaction of this isoenzyme with disulfiram since disulfiram blocks the selective alkylation.