Human stomach alcohol and aldehyde dehydrogenases (ALDH): A genetic model proposed for ALDH III isozymes

Isozyme phenotypes of alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH) from human gastroendoscopic as well as surgical gastric biopsies were determined by starch gel electrophoresis and agarose isoelectric focusing. γγ ADH isozymes were expressed predominantly in the mucosal layer of the stomach, whereas ββ isozymes were in the muscular layer. In the 56 gastroendoscopic mucosal biopsies examined, the homozygous ADH₃ 1-1 phenotype was found in 75% of the samples, and the heterozygous ADH₃ 2-1 phenotype in 25%. Accordingly, the gene frequencies of the allelesADH ₃ ¹ andADH ₃ ² were calculated to be 0.88 and 0.12, respectively. Using a modified agarose isoelectric focusing procedure, gastric ALDH I, ALDH II, and up to five ALDH III forms could be clearly resolved. The ALDH III isozymes accounted for more than 80% of the total ALDH activities in gastric mucosa and exhibitedK _m values in the millimolar range for propionaldehyde atpH 9.0. Forty-five percent of the 55 gastroendoscopic biopsies studied lacked ALDH I isozyme. The complex gastric ALDH III isozyme phenotypes seen in these biopsies fall into three patterns. They can be interpreted by a genetic hypothesis, based on a dimeric molecule, in which there are two separate genes,ALDH _3a andALDH _3b, with theALDH _3b locus exhibiting polymorphism. The homozygous phenotypes ALDH_3b 1-1 and ALDH_3b 2-2 were found to be 4 and 76%, respectively, and the heterozygous ALDH_3b 2-1 phenotype 20%, of the total. Therefore, the allele frequencies forALDH _3b ¹ andALDH _3b ² were calculated to be 0.14 and 0.86, respectively. Several lines of biochemical evidence consistent with this genetic model are discussed. This work was supported by grants from the National Science Council, Republic of China, and the Institute of Biomedical Sciences, Academia Sinica.