[x-(Adenosyl)alkyl]cobalamins (homoadenosylcobalamins) are useful ana-logues of adenosylcobalamin to get information about the distance between Co and C5¢, which is critical for Co-C bond activation. In order to use them as probes for exploring the active sites of enzymes, the coenzymic properties of homoadenosylcobalamins for diol dehydratase and ethanol-amine ammonia-lyase were investigated. The kcat and kcat ⁄Kmvalues for adenosylmethylcobalamin were about and that for the regu-lar coenzyme with diol dehydratase, respectively. .
