ESSENTIAL LYSINE RESIDUE IN GLUTATHIONE-REDUCTASE - CHEMICAL MODIFICATION BY PYRIDOXAL 5'-PHOSPHATE

Yeast glutathione reductase was inactivated by pyridoxal 5'-phosphate. The inhibition was reversed by dilution. The enzyme-pyridoxal 5'-phos phate complex on reduction with sodium borohydride gave a characterist ic absorption maximum at 325 nm and fluoresence maximum at 395 nm when exciated at 325 nm. These results were consistent with the reaction o f epsilon-amino group of lysine residue of the enzyme with pyridoxal 5 '-phosphate. The enzyme was protected against pyridoxal 5'-phosphate i nhibition by NADP indicating thereby that the essential lysine residue s are present around the NADP binding site.