Inactivation of Bacillus stearothermophilus leucine aminopeptidase II by hydrogen peroxide and site-directed mutagenesis of methionine residues on the enzyme

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Title:	Inactivation of Bacillus stearothermophilus leucine aminopeptidase II by hydrogen peroxide and site-directed mutagenesis of methionine residues on the enzyme
Authors:	Kuo, L.-Y.ac, Hwang, G.-Y.ab, Yang, S.-L.d, Hua, Y.-W.d, Chen, W.d, Lin, L.-L.d
Contributors:	Department of Life Science, Tunghai University
Keywords:	Bacillus stearothermophilus;Chemical oxidation;Leucine aminopeptidase;Methionine;Site-directed mutagenesis
Date:	2004
Issue Date:	2013-05-14T09:00:47Z (UTC)
Abstract:	Leucine aminopeptidases (LAPs) are exopeptidases that remove the N-terminal L-leucine from peptide substrates. Oxidative stability assay showed that the recombinant Bacillus stearothermophilus LAP II (rLAPII) was sensitive to oxidative damage by hydrogen peroxide at the elevated temperature. The H 2O2-treated enzyme experienced obvious changes in the secondary structure when the oxidant concentration increased to 300 mM. To investigate the role of methionine residues on the oxidative inactivation, each of the five methionine residues in the rLAPII was replaced with leucine by site-directed mutagenesis. The mutant enzymes with an apparent Mr of approximately 44.5 kDa were overexpressed in Escherichia coli and were purified to homogeneity by nickel-chelate chromatography. The specific activities for Met82Leu, Met88Leu, Met254Leu, and Met382Leu were similar to that of the wild-type enzyme, whereas a reduced activity was observed in Met136Leu. The 50% decrease in the catalytic efficiency (kcat/Km) for Met136Leu was caused by 47% decrease in kcat value. As compared with the wild-type enzyme, all mutant proteins were more sensitive to the oxidant, implying that the methionine residues of B. stearothermophilus LAP II are important for the protection of the enzyme from oxidative inactivation. ? 2004 Plenum Publishing Corporation.
Relation:	Protein Journal Volume 23, Issue 4, 2004, Pages 295-302
Appears in Collections:	[生命科學系所] 期刊論文

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