Two new dehydrogenase structures, the 354-residue polypeptide chain of sorbitol dehydrogenase (from sheep liver) and the 500-residue polypeptide chain of cytoplasmic aldehyde dehydrogenase (from human liver), have blocked N-termini. The N-terminal peptides were purified by reverse-phase high-performance liquid chromatography and submitted to mass spectrometry after derivatization. They were also analyzed by dipeptidyl carboxypeptidase digestion, utilizing gas chromatography-mass spectometry for dipeptide identifications. Results are consistent and establish that sorbitol dehydrogenase has N-terminal acetylalanine and aldehyde dehydrogenase N-terminal acetylserine in amino acid sequences that are compatible with estimates from chemical analyses. The two N-terminal residues found are typical of acetylated proteins in general, extend the group of known acetylated dehydrogenases, and show that these intracellular proteins are frequently N-terminally acetylated.
