Cobalamin ligation and interaction with sodium dodecyl sulfate and bovine serum albumin studied by 31P and 13C NMR

Abstract

Carbon-13 nuclear magnetic resonance has been employed to study the ligation modes of hydroxycobalamin by K 13CN and NaS 13CN. The pH and temperature dependence of di( 13C) cyanocobalamin spectra reveal the presence of a kinetic trans effect which labilizes the coordinated cyanides in this complex. The carbon spectra are utilized in conjunction with phosphorus-31 nmr of the phosphodiester in the benzimidazole side arm to establish correlations between the spectra and the coordination state of the cobalamin. It is found that this phosphorous resonance indicates the benzimidazole coordination state by virtue of its resonance position and serves as a probe of pH dependent properties of cobalamin. 31P nmr is further demonstrated to be capable of reporting upon the coordination state of cobalamins in their interaction with the detergent sodium dodecyl sulfate and the cobalamin binding protein, bovine serum albumin, indicating its potential for reporting upon enzyme intermediates of vitamin B 12 dependent enzymes.