Toward bifunctional antibody catalysis.

Antibodies that catalyze the deprotonation of unactivated benzisoxazoles to give the corresponding salicylonitriles were prepared using as antigen a 2-aminobenzimidazolium derivative coupled to a carrier protein via its benzene ring. The hapten was designed to induce an antibody binding site with both a base and an acid, in position to initiate proton transfer and stabilize developing negative charge at the phenoxide leaving group, respectively. Consistent with this design, the catalysts exhibit bell-shaped pH-rate profiles, while chemical modification identified several functional groups that could participate in bifunctional catalysis.

Homoadenosylcobalamins as probes for exploring the active sites of coenzyme B12-dependent diol dehydratase and ethanolamine ammonia-lyase.

[Omega-(Adenosyl)alkyl]cobalamins (homoadenosylcobalamins) are useful analogues 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 ethanolamine ammonia-lyase were investigated. The kcat and kcat/Km values for adenosylmethylcobalamin were about 0.

Homocoenzyme B12 and bishomocoenzyme B12: covalent structural mimics for homolyzed, enzyme-bound coenzyme B12.

Efficient electrochemical syntheses of "homocoenzyme B(12)" (2, Co(beta)-(5'-deoxy-5'-adenosyl-methyl)-cob(III)alamin) and "bishomocoenzyme B(12)" (3, Co(beta)-[2-(5'-deoxy-5'-adenosyl)-ethyl]-cob(III)alamin) are reported here. These syntheses have provided crystalline samples of 2 and 3 in 94 and 77 % yield, respectively. In addition, in-depth investigations of the structures of 2 and 3 in solution were carried out and a high-resolution crystal structure of 2 was obtained.