LOCALIZATION OF A PORPHYRIN-TYPE COMPOUND IN YEAST PLASMA-MEMBRANES AND ITS INVOLVEMENT IN PHOTOSENSITIZATION OF LIPID-PEROXIDATION

Fluorescence of isolated yeast plasma membranes with a peak at 683 nm was recorded and ascribed to a compound absorbing in the visible regio n of the spectrum. The fluorescence excitation spectrum has a maximum at 410 nm and four less intensive peaks in the range of 500-620 nm, wh ich is characteristic of porphyrins. Visible light (400-600 nm) induce s lipid peroxidation in plasma membranes. Intensification of this proc ess when H2O is replaced by D2O and its inhibition by sodium azide are suggestive of the important role of singlet oxygen in initiating phot o-induced oxidative reactions. The most probable candidate for the pho tosensitizer is a membrane-bound porphyrin-type compound.