Bovine Serum Albumin as a Catalyst. II. Characterization of the Kinetics

The accelerated decomposition of the Meisenheimer complex, 1,1-dihydro-2,4,6-trinitrocyclohexadienate, by bovine serum albumin (BSA) is reported in detail. In the pH range of 7-9 the BSA-catalyzed reaction is accelerated by a factor of about 10⁴ relative to the rate of decomposition of the substrate alone. This catalysis requires an unprotonated base on the protein (pK_a = 8.4) and can be stoichiometrically inhibited by binding of 1 equiv of pyridoxal phosphate (PP) to the protein. Chemical modification with acetic anhydride and fluorodinitrobenzene along with previous studies on the PP-BSA complex indicates that the active site of the molecule is rich in lysine and is probably coincident with a unique PP binding site in the protein. This unusual catalytic function has also been used as a sensitive probe to generate new information on some of the ligand-binding properties of the protein.