Complexes of vitamin B6XX: equilibrium and mechanistic studies of the reaction of pyridoxal-5'-phosphate with pyridoxamine-5'-phosphate in the presence of copper(II).

The interaction of Cu(II) with pyridoxamine-5'-phosphate (PMP) and pyridoxal-5'-phosphate (PLP) was studied potentiometrically. The titration data were assessed by MINIQUAD program. Several protonated and nonprotonated complexes have been found to exist in solution. The reaction of PLP with Cu(II)-PMP has been studied kinetically, using the stopped-flow technique. Two rate steps have been observed. The first step has been attributed to the formation of a Schiff's base metal complex. The second step may be due to the formation of a ternary complex formation. A mechanism was suggested.