Identification of a paramagnetic species as an early intermediate in the coenzyme B12‐dependent glutamate mutase reaction A cob(II)amide?

Abstract

Highly active and cobamide‐free glutamate mutase was obtained from Clostridium cochlearium by a modification of the original purification procedure. After incubation of the enzyme with dithiothreitol, adenosylcobalamin (coenzyme B₁₂) and the substrate (S)‐glutamate, a paramagnetic species was observed by EPR‐spectroscopy. The signal was maximal within 15 ms after mixing with glutamate. Different signals were detected after incubating the system with the competitive inhibitors (2S,4S)‐4‐fluoroglutamate or 2‐methyleneglutarate instead of the substrate. The former developed with an at least 100‐fold lower rate then the signal with glutamate. All three signals are probably due to low‐spin cob(II)amide species with an extraordinary low g_xy value as compared with cob(II)alamin.