[Comparative characteristics of membrane forms of aldehyde dehydrogenase]

It was demonstrated from the results of kinetic analysis that acetaldehyde oxidation reaction, which is catalyzed by membrane isoenzyme forms of mitochondrial and microsomal aldehyde dehydrogenases, has the ordered Bi-Bi mechanism. An attempt was made to compare the active site structures of these two isozyme forms using cyclopropylethyl-containing benzoic acid amides which are the reversible inhibitors of the studied enzyme activity. The amides competitively inhibited each enzyme activity relative to acetaldehyde. The inhibition constant values were calculated. As to NAD+ partially competitive type of inhibition was observed for aldehyde dehydrogenase of the microsomes. At low amide concentrations the mitochondrial aldehyde dehydrogenase was inhibited uncompetitively. With increased concentration of the compounds over 75 microM the character of inhibition by 2.4-dichlorine- and 2.4-dichlorine-5-methylbenzoic acid amides changed to mixed one; and when using the amides of 2.5-dichlorine-4-methylbenzoic acid it changes for pseudoinhibition. The difference of kinetic behaviour of the studied compounds with aldehyde dehydrogenase membranes forms suggests the conformation similarity of the sites for binding acetaldehyde for the both enzymes and distinction of the sites for coenzyme binding.