کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
9616774 | 48922 | 2005 | 6 صفحه PDF | دانلود رایگان |
عنوان انگلیسی مقاله ISI
Selectivity of the enzymatic synthesis of ampicillin by E. coli PGA in the presence of high concentrations of substrates
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کلمات کلیدی
موضوعات مرتبط
مهندسی و علوم پایه
مهندسی شیمی
کاتالیزور
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چکیده انگلیسی
Penicillin G acylase (PGA) catalyzes the synthesis/hydrolysis of acyl derivatives of phenylacetic acid through the formation of a covalent intermediate (the acyl-enzyme complex). When used for the kinetically controlled synthesis of β-lactam antibiotics, this enzyme promotes two undesired side reactions: the hydrolysis of the acyl side-chain precursor and of the antibiotic. Therefore, a high selectivity (synthesis/hydrolysis, S/H ratio) is very important for the process economics. Here, the enzymatic synthesis of ampicillin from d-phenylglycine methyl ester (PGME) and 6-aminopenicillic acid (6-APA), using PGA from Escherichia coli (EC 3.5.1.11) is studied. Kinetic assays provided S/H for high concentrations of substrates (up to 200 mM of 6-APA and 500 mM of PGME), using soluble PGA, at 25 °C, pH 6.5. S/H increased with 6-APA concentration, in accordance with the literature. However, when the concentration of 6-APA approached saturation, the rate of enzymatic hydrolysis tended towards zero (i.e., S/H tended to infinity). On the other hand, when the concentration of ester was augmented, S/H consistently decreased. This behavior, to the best of our knowledge still not reported, indicates that the acylation step may occur with 6-APA already positioned for the nucleophilic attack.
ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Journal of Molecular Catalysis B: Enzymatic - Volume 33, Issues 3â6, 1 June 2005, Pages 81-86
Journal: Journal of Molecular Catalysis B: Enzymatic - Volume 33, Issues 3â6, 1 June 2005, Pages 81-86
نویسندگان
Marcelo P.A. Ribeiro, Andrea L.O. Ferreira, Raquel L.C. Giordano, Roberto C. Giordano,