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 (H2O)-H-2 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 (H2O)-H-3, tritium was incorporated preferentially into the product. Glutamate is racemized by the enzyme probably through a two base mechanism.