ON THE SITES OF ATTACHMENT AND REACTION OF ALDEHYDE DEHYDROGEN ASES

Abstract

Investigation of the site of attachment of the two substrates aldehyde and pyridine nucleotide became possible when it was learned that proteolytic destruction of a triphosphopyridine nucleotide (TPN) linked succinic semialdehyde dehydrogenase by trypsin was dependent upon the addition of pyridine nucleotide. The criterion of pyridine nucleotide binding used was the susceptibility to trypsin digestion, and the attachment of substrates to enzyme were investigated. Data is presented to show that TPN is not bound to a protein sulfhydryl group. Under conditions where reduced disulfide groups (arsenite inhibition) and all other available sulfhydryl groups (p-chloromercuribenzoate inhibition) are occupied, TPN still increases the rate of proteolytic inactivation. Nor does TPN compete with arsenite for a place on the enzyme. Characteristics of arsenite-sensitive aldehyde dehydrogenases are described and simple approximations of reaction mechanisms are proposed.