Effects of Culture Medium on Pyridoxine (Pyridoxamine) Phosphate Oxidase Activity in Wheat Callus

Abstract

Modulation of a pyridoxal 5'-phosphate-synthesizing enzyme, pyridoxine (pyridoxamine) phosphate oxidase (EC 1.4.3.5), was investigated in wheat suspension culture. Pyridoxine-HCl added to the culture medium enhanced the pyridoxine 5'-phosphate (PNP) oxidase activity, but not pyridoxamine 5'-phosphate (PMP) oxidase activity. Thiamine-HCl also showed a similar effect. The PNP oxidase activity was most effectively enhanced by potassium nitrate from 40 to 80 mM, which was added to the culture medium as a nitrogen source. On the other hand, PMP oxidase activity was stimulated by ammonium-type nitrogen.