AMINOIMIDAZOLE RIBONUCLEOTIDE CARBOXYLASE: PARTIAL PURIFICATION AND PROPERTIES

Abstract

The enzyme aminoimidazole ribonucleotide carboxylase has been partially purified from chicken livers. A somewhat higher degree of purification was achieved with pigeon liver acetone powder as the starting material. This enzyme carboxylates the ribonucleotide but cannot use the free base, aminoimidazole, as its substrate. An investigation of the requirements for optimal activity reveals that magnesium ions are essential. Inhibition by a variety of reagents which react with sulfhydryl groups indicates their importance in the fixation of carbon dioxide to aminoimidazole ribonucleotide. An exhaustive search revealed that none of the B-vitamin cofactors play a role in this reaction. The lack of an energy requirement, e.g. ATP, for activity and the nucleophilic nature of the amino-substituted ring suggest that the carboxylation of aminoimidazole ribonucleotide proceeds via a direct enzyme-mediated reaction involving Mg++ions and active sulfhydryl groups.