EPR spectra of DDH with anAdoCbl as coenzyme in the presence of (R,S)-1,2-propanediol. The samples were frozen in cold isopentane 10 min after mixing within an anaerobic chamber. (A) Unlabeled coenzyme. (B) [13C5-ribosyl]-anAdoCbl. (C) anAdoCbl and (R,S)-1,2-[2H6]propanediol. Deuterium labeling at C5′ of the coenzyme occurs upon reaction with substrate. Experimental conditions: temperature, 4.5 K; modulation amplitude, 12 G; microwave power 0.2 mW; spectrometer frequency, 9.233 GHz (g=2.0 at 3,299 G). All spectra are an average of four 8 min scans.