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
موضوعات مرتبط
مهندسی و علوم پایه مهندسی شیمی کاتالیزور
پیش نمایش صفحه اول مقاله
Selectivity of the enzymatic synthesis of ampicillin by E. coli PGA in the presence of high concentrations of substrates
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 3–6, 1 June 2005, Pages 81-86
نویسندگان
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