the organometallic h - cluster at the 
 active site of [ fefe]-hydrogenases 
 is synthesized by three accessory proteins , two of which are radical s - adenosylmethionine enzymes ( hyde , hydg ) and one of which 
 is a gtpase ( hydf ) . in this work we probed the specific role of h 
 atom abstraction in hydg - catalyzed carbon monoxide and cyanide production 
 from tyrosine . 
 the isotope distributions of 5-deoxyadenosine 
 and p - cresol were evaluated using deuterium - labeled 
 tyrosine substrates in h2o and d2o . 
 the observation 
 of multiply deuterated 5-deoxyadenosine and deuterated s - adenosylmethionine when the reaction is carried out in 
 d2o provides evidence for a 5-deoxyadenosyl radical - mediated 
 abstraction of a hydrogen atom from a solvent - exchangeable position 
 as a reversible event .