Nanosecond transient absorption spectroscopy of coenzyme B12. Quantum yields and spectral dynamics.

摘要: Photolysis of adenosylcobalamin leads to homolytic cleavage, similar many the B12-dependent enzyme reactions. Therefore, we have used photolysis study structure and lability cobalt-carbon bond. The nanosecond quantum yield for is 0.23 +/- 0.04, higher than reported previously. acidified form adenosylcobalamin, so called "base-off" B12, has a much lower at 0.045 0.015, demonstrating an inverse correlation between bond strength yield. Investigation wavelength dependence shows that there highly efficient transmission energy from corrin ring A comparison transient static spectra showed small spectral differences. any relaxation sterically distorted may be detectable only sub-nanosecond timescales. Spectral analysis also provides data on kinetics recombination. In absence enzyme, geminate rebinding must substantial, since rate Co(II) deoxyadenosyl radical recombination near diffusion controlled limit. it likely functions pull partners apart, perhaps as suggested previously, through conformational change. importance in mechanism cleavage further supported by our results with picosecond absorption studies.