Effect of bovine serum albumin on the water solubility of hydrophobic corrinoids

Medicinal effects of hydrophobic derivatives of vitamin B12 have been insignificantly investigated primarily due to their low solubility in aqueous solutions. One of the ways to increase their water solubility is the complexation with proteins. Here, we report the results of the studies of the reactions between aquacyano cobyrinic acid or monocyano cobesters (i.e., heptamethyl, heptaethyl, heptapropyl, and heptabutyl cobyrinates) and bovine serum albumin (BSA). The weakest binding is observed between aquacyano cobyrinic acid and BSA. In the case of monocyano heptaethyl cobyrinate, one BSA molecule is capable of binding up to six corrinoid molecules preventing its precipitation. Moreover, the pronounced effect of BSA on the solubility in water was observed in the case of monocyano heptapropyl cobyrinate. The absence of the precipitation of monocyano heptabutyl cobyrinate was observed only in the presence of high excess of BSA. BSA modification by diethyl pyrocarbonate, a chemical predominantly reactive toward imidazole motifs, indicated that a major fraction of BSA is bound with monocyano heptaethyl, heptapropyl, and heptabutyl cobyrinates via histidine residues. We showed that nitrosyl complexes of heptaethyl and heptapropyl cobyrinates can be stabilized from precipitation in aqueous solutions using BSA.