Isolation of high-Km aldehyde dehydrogenase isoenzymes from human gastric mucosa

Human stomach aldehyde dehydrogenase-3 isoenzymes were isolated by DEAE-cellulose, CM-Sephadex, and 5' AMP-Sepharose chromatographies to apparent homogeneity. The subunit of the isoenzymes was determined to be 55,000 daltons by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The kinetic constants for oxidation of various aliphatic and aromatic aldehydes were determined. The Km value for straight-chain aldehydes decreased over 9,000 fold when chain length increased from C2 to C7. The Vmax/Km value for heptaldehyde was 10-fold higher than that for benzaldehyde. NAD+ was a much better cosubstrate than NADP+. The human stomach aldehyde dehydrogenase-3 isoenzymes were insensitive to disulfiram inhibition and were not activated or inhibited by magnesium ions.