Kinetic studies of rat liver glutamicalanine transaminase.

With the discovery that pyridoxal phosphate and pyridoxamine phosphate were cofactors for enzymatic transamination, it was proposed that the reaction was biphasic, involving first an amino group transfer from the amino acid substrate to enzymebound pyridoxal phosphate, followed by a transfer of the amino group to the keto acid substrate (for review, see (1)). With the availability of a highly purified transaminase, Jenkins and Sizer (2) were able to study individual half-reactions and obtained results consistent with the proposed role of pyridoxal as an amino group carrier. These experiments, however, were unable to distinguish between the alternatives of a single enzymatic site for all substrates versus two sites of attachment, each specific for a keto acid-amino acid pair.l More recently, the extensive kinetic studies of Velick and Vavra (5) with glutamic-aspartic transaminase of pig heart have ruled out certain types of two-site mechanisms for this enzyme and have led to the proposal of a single site of attachment of all substrates as the most attractive mechanism. Similar kinetic studies have been performed with a highly purified glutamic-alanine transaminase of rat liver (6) and are reported in the present communication.