Isolation and characterization of aldehyde dehydrogenase isozymes from usual and atypical human livers

Usual human livers contain two major aldehyde dehydrogenase isozymes, cytosolic ALDH1 component and mitochondrial ALDH2 component, while human livers with "atypical" phenotype have only ALDH1 isozyme and are missing ALDH2 isozyme. Approximately 50% of orientals are atypical in respect to ALDH isozymes. We previously demonstrated an existence of enzymatically inactive but immunologically cross-reactive material (CRM) in atypical oriental livers. ALDH1 and ALDH2 isozymes were purified to homogeneity from usual livers, and ALDH1 and CRM were purified from atypical oriental livers. Amino acid compositions of ALDH1 and ALDH2 were similar to, but not identical with, each other. Amino acid compositions of ALDH2 and CRM were identical within analytical errors. Subunit molecular size of ALDH1 estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis was 56,200 daltons, and that of ALDH2 was 52,600 daltons. The two isozymes did not contain a common subunit. Subunit molecular weight of CRM was identical with that of ALDH2. Double immunodiffusion precipitation revealed that ALDH1 and ALDH2 were immunologically analogous but not identical, and that CRM and ALDH2 were immunologically indistinguishable. These results support the genetic model that CRM is an abnormal defective protein resulting from a mutation of the ALDH2 locus.