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Enantioselective Reductive Amination of α-Keto Acids by Papain-Based Semisynthetic Enzyme

Chun-Xiang Chen1, Bo Jiang1, C. Branford-White2, and Li-Min Zhu1*

1College of Chemistry, Chemical Engineering and Biotechnology, Donghua University, Shanghai 201620, China; fax: 0086-21-6779-2655; E-mail: lzhu@dhu.edu.cn

2Institute for Health Research and Policy, London Metropolitan University, 166-220 Holloway Road, London, N7 8DB, UK

* To whom correspondence should be addressed.

Received February 19, 2008; Revision received July 29, 2008
Alkylation of a cysteine residue in papain with a pyridoxamine (PX) cofactor was carried out. The resulting semisynthetic enzyme (papain–PX) has no detectable protease activity but has the ability to catalyze enantioselective reductive amination of α-keto acids. The conjugate was characterized by ion-exchange chromatography, and the optimal reaction conditions were found. We report that papain–PX reductively aminates the alkyl side chain of functionalized α-keto acids to give the respective α-amino acids with high enantioselectivities, greater than 70%. Based on these studies, we propose a new model for the catalytic activity of the semisynthetic enzyme with Interchem software. The results of the study demonstrate the effectiveness of the modified enzyme and its potential for engineering new catalytic specificity.
KEY WORDS: semisynthetic enzyme, papain, pyridoxamine, chemical modification

DOI: 10.1134/S0006297909010052