Utilizing an intrinsic 31P NMR probe in studies of cobalamin ligation

The inorganic chemistry of the cobalt corrinoids - an update

The inorganic chemistry of the cobalt corrinoids, derivatives of vitamin B₁₂, is reviewed, with particular emphasis on equilibrium constants for, and kinetics of, their axial ligand substitution reactions. The role the corrin ligand plays in controlling and modifying the properties of the metal ion is emphasised. Other aspects of the chemistry of these compounds, including their structure, corrinoid complexes with metals other than cobalt, the redox chemistry of the cobalt corrinoids and their chemical redox reactions, and their photochemistry are discussed. Their role as catalysts in non-biological reactions and aspects of their organometallic chemistry are briefly mentioned. Particular mention is made of the role that computational methods - and especially DFT calculations - have played in developing our understanding of the inorganic chemistry of these compounds. A brief overview of the biological chemistry of the B₁₂-dependent enzymes is also given for the reader's convenience.

Inactivation of B12 and folate coenzymes by butyl nitrite as observed by NMR: implications on one-carbon transfer mechanism

The effects of butyl nitrite, a frequently used recreational drug, on methyl cobalamin and 5-methyl tetrahydrofolate were investigated by using 1H and 31P NMR spectroscopies. While no effect could be observed in organic solvents, strong interactions of butyl nitrite with the methyl cobalamin and 5-methyl tetrahydrofolate were found to occur in water. Butyl nitrite decomposes in water generating H+ and NO-2. The former protonates to give the "base-off" configuration of methyl cobalamin while the Co-CH3 bond is cleaved. Similarly, the methyl group at the 5N position and the pyrazine ring of 5-methyl tetrahydrofolate were found to be affected by butyl nitrite. The overall interaction of butyl nitrite with both coenzymes shows displacement of the methyl group and derivatization or destruction of the coenzymes that may lead to deficiencies of both B-12 and/or folates.

31p nuclear relaxation studies of para- and diamagnetic cobalamins in their two isomeric forms

A new, naturally occurring isomeric form of vitamin B-12 was reported by us earlier (Katada, M., Tyagi, S., Nath, A., Petersen, R.L. and Gupta, R.K. (1979) Biochim. Biophys. Acta 584, 149-163). The Mössbauer parameters of various derivatives of vitamin B-12, including the one-electron reduced species, cob(II)-alamin (vitamin B-12r), exhibit differences for the two isomeric forms. This and some other observations from our laboratory indicated that the new form (vitamin B-12') presumably constitutes a conformational isomer possessing a different puckering of the corrin ring. The 31P nuclear relaxation studies of vitamins B-12r and B-12'r, B-12 and B-12', and dicyanocobalamin as compared to dicyanocobalamin' reported here are consistent with our earlier conjecture. The relaxation of the 31P nucleus in cob(II)alamins is primarily due to its dipolar interaction with the paramagnetic cobalt and therefore the measurement of the 31P nuclear relaxation times (T1) in the two isomeric forms permits us to calculate Co(II)-31P distances. The Co(II)-31P distance in vitamin B-12'r is found to be larger than that in vitamin B-12r. The 31P T1 value in the diamagnetic cob(III)-alamins is determined predominantly by its dipolar interaction with the two closest protons flanking the phosphate group, one being situated on the ribose moiety and the other on the amino propanol group. The nuclear relaxation times T1 of cyanocobalamin and dicyanocobalamin differ from ;those of their corresponding conformational isomers. The observed differences in 31P relaxation rates of the para- and diamagnetic cobalamins in their two isomeric forms can be understood on the basis of structural changes arising from variations in the nature of puckering of the corrin ring. The 31P chemical shifts in the two isomers remain essentially unchanged, indicating that the structural differences in the isomeric forms do not alter the electronic environment of the phosphorus nucleus.