D2O-alanine exchange reactions catalyzed by alanine racemase and glutamic pyruvic transminase |
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Authors: | U M Babu R B Johnston |
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Institution: | Department of Chemistry University of Nebraska Lincoln, Nebraska 68508 USA |
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Abstract: | NMR studies in D2O (>90%) reveal that Alanine Racemase (5.1.1.1.) from catalyzes the exchange of the α hydrogen of - and -alanine with D2O. Glutamic Pyruvic Transaminase (2.6.1.2.) and Glutamic Oxaloacetic Transaminase (2.6.1.1.) catalyze the exchange of α and β hydrogens of -alanine. The rates of exchange of α and β hydrogens appear to be of the same order of magnitude. The transaminase catalyzed exchange is enhanced by catalytic amounts of pyruvate. The side chain of -alanine is held more rigidly at the active site of transaminase so that the planar conjugated system can be extended to include the α and β carbons. A generalized mechanism is proposed for the action of pyridoxal phosphate dependent transaminases which extends Braunstein and Snell mechanism to include the structures which contribute to the labilization of β hydrogens of amino acids by the transaminases that have been studied. |
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