THE MECHANISM OF GLUTAMATE MUTASE - AN UNUSUALLY SUBSTRATE-SPECIFIC ENZYME

Coenzyme B-12-dependent glutamate mutase catalyses the interconversion of (2S)-glutamic acid and (2S, 3S)-3-methylaspartic acid. The enzyme is unable to accept alternative substrates for the rearrangement react ion but is inhibited by substrates analogues including (2S, 3R)- and ( 2S, 3S)- and (2S, 3S)-3-methylglutamic acid, 2-bromo-2, 3-methanosucci nic acid, (2S)-homocysteic acid. The primary isotope effect upon V-max and V/K for the isomerisation of the (2S)-glutamic acid is 3.7 +/- 0. 2 and 13.5 +/- 1.0 respectively. There are two C-H bond breaking steps involved in the isomerization reaction. The relative sizes of V-D and (D)(V/K) indicate that neither of these steps are cleanly rate limiti ng.