Co-C bond activation in methylmalonyl-CoA mutase by stabilization of the post-homolysis product Co2+ cobalamin.

Despite decades of research, the mechanism by which coenzyme B12 (adenosylcobalamin, AdoCbl)-dependent enzymes promote homolytic cleavage of the cofactor's Co-C bond to initiate catalysis has continued to elude researchers. In this work, we utilized magnetic circular dichroism spectroscopy to explore how the electronic structure of the reduced B12 cofactor (i.e.

Electronic structure studies of the adenosylcobalamin cofactor in glutamate mutase.

Glutamate mutase (GM) is a cobalamin-dependent enzyme that catalyzes the reversible interconversion of L-glutamate and L-threo-3-methylaspartate via a radical-based mechanism. To initiate catalysis, the 5'-deoxyadenosylcobalamin (AdoCbl) cofactor's Co-C bond is cleaved homolytically to generate an adenosyl radical and Co2+ Cbl. In this work, we employed a combination of spectroscopic and computational tools to evaluate possible mechanisms by which the Co-C bond is activated for homolysis.

Spectroscopic and computational studies on the adenosylcobalamin-dependent methylmalonyl-CoA mutase: evaluation of enzymatic contributions to Co-C bond activation in the Co3+ ground state.

Methylmalonyl-CoA mutase (MMCM) is an enzyme that utilizes the adenosylcobalamin (AdoCbl) cofactor to catalyze the rearrangement of methylmalonyl-CoA to succinyl-CoA. Despite many years of dedicated research, the mechanism by which MMCM and related AdoCbl-dependent enzymes accelerate the rate for homolytic cleavage of the cofactor's Co-C bond by approximately 12 orders of magnitude while avoiding potentially harmful side reactions remains one of the greatest subjects of debate among B(12) researchers. In this study, we have employed electronic absorption (Abs) and magnetic circular dichroism (MCD) spectroscopic techniques to probe cofactor/enzyme active site interactions in the Co(3+)Cbl "ground" state for MMCM reconstituted with both the native cofactor AdoCbl and its derivative methylcobalamin (MeCbl).

Spectroscopic and computational studies of Co3+-corrinoids: spectral and electronic properties of the B12 cofactors and biologically relevant precursors.

The B(12) cofactors methylcobalamin (MeCbl) and 5'-deoxyadenosylcobalamin (AdoCbl) have long fascinated chemists because of their complex structures and unusual reactivities in biological systems; however, their electronic absorption (Abs) spectra have remained largely unassigned. In this study, we have used Abs, circular dichroism (CD), magnetic CD (MCD), and resonance Raman spectroscopic techniques to probe the electronic excited states of Co(3+)Cbl species that differ with respect to their upper axial ligand, including MeCbl, AdoCbl, aquacobalamin (H(2)OCbl(+)), and vitamin B(12) (cyanocobalamin, CNCbl). Also included to probe the effect of the lower axial ligand on the electronic properties of Cbls is Ado-cobinamide (AdoCbi(+)), an AdoCbl derivative that lacks the tethered base 5,6-dimethylbenzimidazole (DMB) and instead binds a water molecule in the lower axial position.