title: 5'-Peroxyadenosine and 5'-peroxyadenosylcobalamin as intermediates in the aerobic photolysis of adenosylcobalamin.
abstract: The photolysis of adenosylcobalamin (coenzyme B12) results in homolytic cleavage of the Co-C5' bond, forming cob(II)alamin and the 5'-deoxyadenosyl radical. In the presence of molecular oxygen, it has been proposed that the primary reaction is interception of the 5'-deoxyadenosyl radical by O2 to form adenosine-5'-aldehyde as the product (Hogenkamp, H. P. C., Ladd, J. N., and Barker, H. A. (1962) J. Biol. Chem. 237, 1950-1952). 5'-Peroxyadenosine is here found to be the initial nucleoside product of this reaction and found to decompose to adenosine-5'-aldehyde. Evidence indicates that 5'-peroxyadenosine arises from the hydrolysis of 5'-peroxyadenosylcobalamin, with the formation of cob(III)alamin. 5'-Peroxyadenosine undergoes further decomposition to adenosine-5'-aldehyde as the major final product of aerobic photolysis as well as to adenosine and adenine as minor products. In a cobalamin-dependent process, 5'-peroxyadenosine becomes re-ligated to cob(III)alamin to form 5'-peroxyadenosylcobalamin, which quickly decomposes to adenosine-5'-aldehyde and cob(III)alamin. This is supported by spectrophotometric observations of both rapidly photolyzed adenosylcobalamin and the reaction of cob(III)alamin with excess 5'-peroxyadenosine. 5'-Peroxyadenosine also slowly undergoes cobalamin-independent decomposition to adenosine-5'-aldehyde and the minor products adenosine and adenine. The present study provides a detailed description of the products initially formed when aqueous, homolytically cleaved adenosylcobalamin reacts with molecular oxygen and provides a detailed description of the behavior of those products subsequent to photolysis.
authors.affiliation: Department of Biochemistry, University of Wisconsin-Madison, 1710 University Avenue, Madison, Wisconsin 53726, USA.
authors.forename: Phillip A
authors.initials: PA
authors.lastname: Schwartz
authors.forename: Perry A
authors.initials: PA
authors.lastname: Frey
mesh_terms: D000241:Adenosine / Q000031:analogs & derivatives / Q000737:chemistry; D000332:Aerobiosis; D003038:Cobamides / Q000737:chemistry* / Q000528:radiation effects*; D066298:In Vitro Techniques; D009682:Magnetic Resonance Spectroscopy; D008956:Models, Chemical; D015394:Molecular Structure; D010782:Photolysis; D013053:Spectrophotometry; D014805:Vitamin B 12 / Q000031:analogs & derivatives / Q000737:chemistry
chemical_list: D003038:Cobamides; C000913:cobamamide; D000241:Adenosine; D014805:Vitamin B 12