Reaction mechanism of glutamate racemase, a pyridoxal phosphate-independent amino acid racemase.
Glutamate racemase of Pediococcus pentosaceus contained no cofactor, and was completely inactivated by a thiol reagent. The role of a cysteine residue in the enzyme reaction was studied by chemical modification. The modification of this cysteine residue resulted in a concomitant loss of activity. DL-Glutamate protected the enzyme from inactivation. The inactivated enzyme was reactivated by addition of dithiothreitol. The racemization in 2H2O showed an overshoot in the optical rotation of glutamate before the substrate was completely racemized. This indicates that the removal of alpha-hydrogen is the rate determining step. During the racemization of D- or L-glutamate in 3H2O, tritium was incorporated preferentially into the product. Glutamate is racemized by the enzyme probably through a two base mechanism.
Institute for Chemical Research, Kyoto University.
S Y
SY
Choi
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N
Esaki
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T
Yoshimura
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Soda
D000591:Amino Acid Isomerases / Q000737:chemistry* / Q000187:drug effects; D001426:Bacterial Proteins / Q000737:chemistry* / Q000187:drug effects; D003545:Cysteine / Q000737:chemistry; D003903:Deuterium; D004789:Enzyme Activation; D005971:Glutamates / Q000737:chemistry / Q000494:pharmacology; D018698:Glutamic Acid; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D010376:Pediococcus / Q000201:enzymology; D011732:Pyridoxal Phosphate / Q000737:chemistry*; D013438:Sulfhydryl Compounds; D014316:Tritium
D001426:Bacterial Proteins; D005971:Glutamates; D013438:Sulfhydryl Compounds; D014316:Tritium; D018698:Glutamic Acid; D011732:Pyridoxal Phosphate; D003903:Deuterium; D000591:Amino Acid Isomerases; C062292:glutamate racemase; D003545:Cysteine