OXIDATIVE STRESS-RESPONSE IN YEAST - PURIFICATION AND SOME PROPERTIESOF A MEMBRANE-BOUND GLUTATHIONE-PEROXIDASE FROM HANSENULA-MRAKII

Glutathione peroxidase was purified from the total membrane fractions of a yeast, Hansenula mrakii IFO 0895. The purified enzyme gave a sing le protein band with a molecular mass of 28 kDa on SDS-PAGE. The enzym e showed activity to various lipid hydroperoxides and their methyl est ers. The enzyme was also active toward phosphatidylcholine hydroperoxi de and cholesterol hydroperoxide. Since the enzyme was not active on h ydrogen peroxide, the enzyme was thought to be a kind of glutathione S -transferase, although the purified enzyme did not show the glutathion e-conjugating activity with electrophilic compounds such as 1-chloro-2 ,4-dinitrobenzene and o-dinitrobenzene, which are used as the substrat e of glutathione S-transferase in yeast. The glutathione peroxidase in H. mrakii was then suggested to be a novel type of glutathione peroxi dase in substrate specificity and intracellular localization, being di fferent from those of other sources purified so far.