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1. Biochem Biophys Res Commun. 2012 Apr 27. [Epub ahead of print]

Pseudo-enzymatic hydrolysis of 4-nitrophenyl myristate by human serum albumin.

Ascenzi P, Fasano M.

Interdepartmental Laboratory of Electron Microscopy, University Roma Tre, Via
della Vasca Navale 79, I-00146 Roma, Italy; National Institute of Biostructures
and Biosystems, Viale Medaglie d'Oro 305, I-00136 Roma, Italy.

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)∼0s(-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.

Copyright © 2012. Published by Elsevier Inc.

PMID: 22560903 [PubMed - as supplied by publisher]