Abstract
The reactions of human serum albumin (HSA) with optically active amino acid p-nitrophenyl esters (substrate, S) were examined kinetically at 25°C. The rate data were analyzed in terms of a mechanism involving 1 : 1 complexing (S·HSA) between S and HSA. The dissociation constant (KS in M) and the catalytic rate constant (k2 in S-1) of S·HSA were determined. Among ten substrates examined, the reactions with N-carbobenzoxy-D(L)-alanine p-nitrophenyl esters (N-CBZ-D(L)-AlaNP) were most accelerated by HSA. Results of the reaction in the presence of excess N-CBZ-D(L)-AlaNP over HSA indicated the existence of one strong reactive site on HSA. The effects of the reversible binding of the site-specific drug and the chemical modification by site-specific reagents on the HSA activity showed that the reactive site towards N-CBZ-D(L)-AlaNP is the R site located near tyrosine-411 residue of HSA.
