Localization of Cysteine 302 at the Active Site of Aldehyde Dehydrogenase

Abstract

The superreactive cysteine was first identified in human cytoplasmic aldehyde dehydrogenase El isozyme, before its primary structure was known, as a part of 35 residue tryptic peptide (Hempel, 1981; Hempel and Pietruszko, 1981; Hempel et al., 1982) by employing iodoacetamide. When the primary structures of the El and E2 isozymes were established (Hempel et al., 1984, 1985; Hsu et al., 1985), this cysteine was found to occupy position 302 in a 500 amino acid residue polypeptide chain. Iodoacetamide fulfilled all criteria for an aldehyde-competitive, active-site-directed reagent with the exception of total inactivation of the mitochondrial E2 isozyme. Since that time, other investigators have also attempted to identify active site residues. Coenzyme-based affinity reagents (von Bahr-Lindstrom et al., 1985) identified cysteines 369 and 302, Nethylmaleimide identified cysteine 49 and 162 (Tu and Weiner, 1988 a,b) and dimethylaminocinnamaldehyde identified serine 74 (Loomes et al., 1990). Our laboratory developed a substrate-based affinity reagent, bromo-acetophenone (MacKerell et al., 1986), which identified glutamate 268 (Abriola et al., 1987).