Studies on the enzymology of aldehyde dehydrogenase-2 in genetically modified HeLa cells

The Asian flush reaction is known to result from a lysine for glutamine substitution in the aldehyde dehydrogenase 2 (ALDH2) gene. This mutation was studied in HeLa cells transduced with retroviruses carrying the ALDH2E (wild-type) and ALDH2K (variant) cDNAs. The cells expressed high levels of the enzyme protein that had the same pI and enzymatic characteristics as the corresponding liver enzyme. When cells expressing ALDH2E were transduced with ALDH2K expressing retrovirus, the ALDH2 activity was reduced roughly in proportion to the amount of ALDH2K mRNA expressed, indicating a dominant suppression of activity. The half-life of the wild-type enzyme was 22 hr, while that of variant enzyme was 14 hr. The half-life of the enzyme in cells expressing both cDNAs was 13 hr, indicating that the shorter half-life of the variant was also dominant These data are consistent with a model in which the wild-type homodimers have normal activity and turnover, while the heterodimers have reduced to virtually no activity and increased turnover. The model predicts residual ALDH2 activity in heterozygotes of about 13% of that in individuals homozygous for ALDH2*1, in good agreement with experimentally determined values.