Abstract
Chemical modification (N-Arylcarbonylation) of bovine serum albumin (BSA) by N-succinimidyl benzoates (1) was studied kinetically at 25°C and 7.0≤pH≤9.0. The initial rate for the N-arylcarbonylation was expressed as Vi=k2 [BSA] [1]. The second order rate constant, k2, roughly correlated with Hammett σ value for the N-arylcarbonylation by meta-substituted (1), giving positive ρ value. However, the rates for ortho-substituted (1) were slower than those expected from strength of the corresponding benzoic acids because of the steric hindrance. The pH profiles gave slopes of less than unity because the amino groups in BSA are not equivalent. The rate ratios, 10-3k2/k1, d, [where k1, d is the first order rate constant for the decomposition of (1)] were larger than unity for all cases, and the ratios maximized at about pH 8.5 for meta-substituted (1) and ortho-fluoro- (1), however, they decreased with increasing pH for ortho-chloro- and bromo- (1). From the above observations, (1) is concluded to be applicable as an N-arylcarbonyl reagent to the chemical modification of Lys residues in proteins.
