Acetyl‐blocked N‐terminal structures of sorbitol and aldehyde dehydrogenases

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Abstract
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.