Usual human livers contain two major aldehyde dehydrogenase [(ALDH) aldehyde:NAD+ oxidoreductase] isozymes-i.e., a cytosolic ALDH1 component and a mitochondrial ALDH2 component-whereas o50% of Orientals are "atypical" and have only the ALDH1 isozyme and are missing the ALDH2 isozyme. We previously demonstrated that atypical livers contain an enzymatically inactive but immunologically crossreactive material (CRM) corresponding to the ALDH2 component. The enzymatically active ALDH2 obtained from a usual liver and the CRM obtained from an atypical liver were reduced, S-carboxymethylated, and digested by trypsin. Separation of their digests by high-performance reverse-phase chromatography and by two-dimensional paper chromatography and electrophoresis revealed that ALDH2 contained a peptide sequence of -Glu-Leu-Gly-Glu-Ala-GlyLeu-Gln-Ala-Asn-Val-Gln-Val-Lys-and that the glutamine adjacent to lysine was substituted by lysine in CRM. AU other tryptic peptides, including eight peptides containing S-carboxymethylcysteine, were common in ALDH2 and CRM. It is concluded that a point mutation in the human ALDH2 locus produced the glutamine -I lysine substitution and enzyme inactivation. (1, 2). The specific activity of the atypical /82P2 isozyme is nearly 100 times higher than that of the usual P1P, isozyme (2). It has been shown that the active site cysteine of the usual P, subunit is replaced by histidine in the superactive atypical P2 subunit (2).Virtually all Caucasians have two major ALDH isozymes-i.e., ALDH1 and ALDH2 in their livers-whereas =50% of Orientals are "atypical" in that they have only ALDH1 and are missing ALDH2 (3, 4). A very high incidence (50-80%) of acute alcohol intoxication in Orientals could be related to the absence of active ALDH2 and the presence of superactive PA22 alcohol dehydrogenase isozyme (1, 3). However, the atypical Orientals have an enzymatically inactive but immunologically crossreactive material (CRM) in their livers (5). The amino acid composition, subunit molecular size, and immunological characteristics of CRM were indistinguishable from the corresponding properties of ALDH2 but differed from those of ALDH1 (6). Therefore, CRM should be an abnormal defective protein resulting from a mutation of the ALDH2 locus. Genetic study indicates that two common alleles-i.e., ALDH12 for the usual ALDH2 isozyme and atypical ALDH22 for the defective CRM at the same locus-are codominantly expressed in Orientals (7). The present paper reports the molecular difference between the usual ALDH2 and the enzymatically inactive CRM. MATERIALS AND METHODSALDH and CRM. Two ALDH isozymes-i.e., ALDH1 and ALDH,-were purified from autopsy specimens of human liver as described (6). CRM and ALDH1 were purified from atypical Japanese livers, which contained the ALDH1 isozyme but not the active ALDH2 isozyme, as described (6). Purities of the samples were checked by polyacrylamide gel electrophoresis in the presence of NaDodSO4 as described (6). The proteins were thoroughly dialyzed against water and lyoph...

No abstract

No abstract

No abstract

No abstract