title: Pseudo-enzymatic hydrolysis of 4-nitrophenyl myristate by human serum albumin.
abstract: 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: 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 × [NphOMy] and [NphOMy] ≥ 5 × [HSA] match very well each other. The deacylation process is rate limiting in catalysis (i.e., k(+3) << k(+2)) and k(-2)~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.
authors.affiliation: Interdepartmental Laboratory of Electron Microscopy, University Roma Tre, Via della Vasca Navale 79, I-00146 Roma, Italy. ascenzi@uniroma3.it
authors.forename: Paolo
authors.initials: P
authors.lastname: Ascenzi
authors.forename: Mauro
authors.initials: M
authors.lastname: Fasano
mesh_terms: D003975:Diazepam / Q000737:chemistry; D004950:Esterases / Q000037:antagonists & inhibitors / Q000737:chemistry*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D009226:Myristates / Q000737:chemistry*; D012709:Serum Albumin / Q000037:antagonists & inhibitors / Q000737:chemistry*
chemical_list: D009226:Myristates; D012709:Serum Albumin; D004950:Esterases; D003975:Diazepam