Acetylation of human serum albumin by p-nitrophenyl acetate.

Human serum albumin reacts very rapidly with p-nitrophenyl acetate (NphOAc). Rapid acetylation of the protein accompanies and largely accounts for the easily observed rapid formation of of p-nitrophenolate ion. One group is acetylated much faster than all others. It appears to be located in a high affinity binding site for small fatty acid anions, to have a pKa of 8.7, and a limiting bimolecular rate of reaction with NphOAc of approximately 3 X 10(4) M-1 sec-1 at alkaline pH values. Rapid reversible binding appears to be a major contributor to the high reaction velocity.