OXIDATIVE STRESS-RESPONSE IN YEAST - GLUTATHIONE-PEROXIDASE OF HANSENULA-MRAKII IS BOUND TO THE MEMBRANE OF BOTH MITOCHONDRIA AND CYTOPLASM

The yeast Hansenula mrakii IFO 0895 induces glutathione peroxidae (GPx ) when the cells are exposed to the oxidative stress such as lipid hyd roperoxide, superoxide- and hydroxy radical-generating conditions. To clarify the localization of GPx in H. mrakii cell, distribution of the enzyme was investigated. After centrifugation of the yeast protoplast homogenates at 2500 X g for 10 min, 67% of total GPx activity was rec overed from the supernatant(Sup. 1) and 33% was from the pellet (Pelle t 1). When the Sup. 1 was fractionated by sucrose density gradient ult racentrifugation, GPx activity was essentially recovered from the mito chondria fraction. Submitochondrial localization of the enzyme showed that 95% and 2.5% of the enzyme was recovered from the inner and outer membrane, respectively. No GPx activity was detected neither in inter membrane space nor in matrix of mitochondria. On the other hand, at le ast 12% of total GPx activity was recovered from the purified plasma m embrane which was obtained from the Pellet 1 by successive sucrose den sity gradient centrifugation, Thus, the GPx of H. mrakii is present in the inner and outer membrane of mitochondria as well as the plasma me mbrane.