화학공학소재연구정보센터
Biochemical and Biophysical Research Communications, Vol.422, No.2, 219-223, 2012
Pseudo-enzymatic hydrolysis of 4-nitrophenyl myristate by human serum albumin
Most of the esterase properties of human serum albumin (HSA) are the result of multiple irreversible chemical modifications rather than turnover. The HSA-catalyzed hydrolysis of 4-nitrophenyl myristate (NphOMy) is consistent with the minimum three-step mechanism involving the acyl-enzyme intermediate HSA-OMy: HSA + NphOMy (k+1)reversible arrow(k-1) HSA:NphOMy (k+2)reversible arrow(k-2) HSA-OMy +NphOH (k+3)reversible arrow(k-3) HSA + MyOH Under all the experimental conditions, values of K-s (= k(-1)/k(+1)), k(+2), and k(+2)/K-s determined under conditions where [HSA] >= 5 x [NphOMy] and [NphOMy] >= 5 x [HSA] match very well each other. The deacylation process is rate limiting in catalysis (i.e., k(+3) <= k(+2)) and k(-2) similar to k(-3) 0 s(-1). The pH dependence of k(+2)/K-s, k(+2), and K-s reflects the acidic pK(a)-shift of one ionizing group from 8.9 +/- 0.2 in NphOMy-free HSA to 6.8 +/- 0.3 in the HSA:NphOMy adduct. The HSA-catalyzed hydrolysis of NphOMy is inhibited competitively by diazepam, indicating that Tyr411 is the active-site nucleophile. (C) 2012 Elsevier Inc. All rights reserved.