Interaction of cysteine with vitamin B12a: kinetic and thermodynamic investigations

Abstract

Rate and equilibrium constants for the interaction of L-cysteine with vitamin B_12a have been determined in aqueous solutions in the absence and in the presence of air as functions of pH, buffer concentration, and temperature. Kinetic treatment of the data has afforded the pH-independent rate constants for the anation of aquo- and hydroxocobalamins by L-cysteine, for the aquation of the vitamin B₁₂–L-cysteine complexes, and for the formation of vitamin B_12r from the L-cysteine complex of vitamin B_12a. The mechanism of these reactions is discussed.