KINETIC-STUDY OF THE REACTION OF PYRIDOXAL 5'-PHOSPHATE WITH HYDRAZINO COMPOUNDS OF PHARMACOLOGICAL ACTIVITY

The kinetics of the reaction between pyridoxal 5'-phosphate (PLP) with carbidopa, hydralazine, and isoniazid, in aqueous solution at variabl e pH and constant ionic strength of 0.1M was studied spectrophotometri cally. The rate constants of formation and hydrolysis of the resulting Schiff base, and its stability were determined in a wide rang of pH. A comparison is made of the formation rate constants with those of PLP with hydrazine. The reactivity shows the sequence isoniazid > hydrazi ne > carbidopa > hydralazine in the whole range of pH studied. The Sch iff bases studied are more stable than those formed by PLP and hexylam ine and as stable as those described for the reactions of PLP with pol y(L-lysine) or copolypeptides containing L-lysine.