Purification and Biochemical Characterization of N-methyl-Histidylesterase from Camel （Camelus dromedarius） Liver  

作　　者：Manal H. A. Ahmad Ghaleb M. Abuerreish 

机构地区：[1]Department of Biological Sciences, Faculty of Science, University of Jordan, Amman 11942, Jordan

出　　处：《Journal of Chemistry and Chemical Engineering》2011年第8期671-683,共13页化学与化工（英文版）

摘　　要：Camel Liver Esterase （LE） was isolated through five consecutive steps： Extraction with Tris/HCl buffer, pH 8, precipitation with ammonium sulfate, affinity chromatography on Affi-gel-butyric acid and on Affi-gel-oleic acid, and preparative polyacrylamide gel electrophoresis （PAGE）. The Km values were found as： methyl butyrate （8.3 mM）, α-naphthyl acetate （3.65 mM）, 13-naphthyl myristate （66.7 mM）, p-nitrophenyl acetate （0.29 mM）, and phenyl acetate （5.26 mM）. The Ki of LE inhibition by bis（4-nitrophenyl） phosphate was 7.9 p.M, and 58 μM by phenyl-methyl-sulfonyl fluoride. The inhibition by these inhibitors is irreversible. p-Hydroxymercuribenzoate or ethylenediamine-tetra-acetic acid did not inhibit the enzyme. LE showed a dimeric structure with molecular weight of 129 kD. The energy of activation of LE was 15.0, 5.5 and 10.75 Kcal, using the substrates： a-naphthyl acetate, p-nitrophenyl acetate, and methyl butyrate, respectively. The optimal pH for LE was between 8 and 10. The N-terminus was found as aspartic acid. The percentage of glycine residues （13.3%） was the highest whereas the percentage of cysteine residues （0.68%） was the lowest in LE. Amino acid composition shows that LE has -50% of its histidine residues as N-methylhistidines.

关 键 词：Camel. Camelus dromedarius Carboxyl esterase ESTERASE Methylhistidyl esterase Methyl-histidine Liver esterase 

分 类 号：Q503[生物学—生物化学] X773[环境科学与工程—环境工程]