Reduction of ATPase activity accompanied by photodecomposition of ergosterol by near-UV irradiation in plasma membranes prepared from Saccharomyces cerevisiae

Abstract

When plasma membranes prepared from the yeast Sacchammyces cerevisiae were exposed to near-UV radiation, photodecomposition of ergosterol and reduction of ATPase activity occurred simultaneously. The V-for ATPase activity decreased markedly with increasing near-UV dosage while the K, value remained constant. When ATPase solubilized from the plasma membrane was exposed to near-UV, the activity remained constant irrespective of dosage, indicating that the ATPase molecule itself was not damaged by near-UV irradiation. The relationship between content of ergosterol and ATPase activity was examined using liposomes constructed with lipids extracted from the membrane. Maximum activity of ATPase was seen at 5% ergosterol in Iiposomes; this activity was 2.5 times greater than that in liposomes without ergosterol. Activity of ATPase bound to liposomes with 5% ergosterol was reduced after near-UV irradiation, while the activity remained unchanged in the case of the liposomes without ergosterol. Fluidity of the liposomes with 5 YO ergosterol also decreased with increasing near-UV dosage. Dosage-response curves for reduction of ATPase activity and for decrease in fluidity were similar to that for photodecomposition of ergosterol. These results suggested that the reduction of ATPase activity in the membrane by near-UV irradiation was not caused by photochemical degradation of the primary structure of the ATPase molecule, but was attributable to conformational change resulting from an alteration in the higher-order structure of the membrane due to photochemical decomposition of ergosterol.

Implications of deletion and membrane ergosterol content for glycerol efflux from

“…The results presented here suggest that ergosterol may play an important role in glycerol e¥ux and survival of S. cerevisiae yeast cells during osmotic downshock. Liposomes prepared from yeast plasma membrane lipids likewise required an adequate level of ergosterol in order to maintain membrane £uidity, which decreased with a reduction of ergosterol content [33]. The importance of ergosterol for glycerol transport has also been reported for C. albicans, where mutants inhibited in ergosterol synthesis exhibited decreased permeability for glycerol [6].…”

“…However, the mechanisms by which ergosterol improves glycerol release as well as survival of yeast cells are not yet clear. It could presumably be related to the membrane stabilising e¡ects of ergosterol [34] and the associated improvements in membrane £uidity [33]. Further work is required to elucidate the precise mechanism of ergosterol involvement in glycerol e¥ux and survival of yeast cells after osmotic downshock.…”

Effects of singlet oxygen on membrane sterols in the yeast Saccharomyces cerevisiae

“…Künemund and Höfer [40] have shown that the permeability to cations is greatly reduced in a Rhodotorula gracilis mutant defective in ergosterol biosynthesis compared with the yeast wild‐type strain indicating that the sterol content of the plasma membrane plays an important role in its permeability properties. Furthermore, it has been observed that photochemical decomposition of ergosterol in the plasma membranes of S. cerevisiae induced by UV light is accompanied by a reduction of ATPase activity [41]. Recently it has been demonstrated that the function of the multi drug resistance pump, Pdr5p, is reduced in S. cerevisiae strains bearing disruptions in the ergosterol biosynthetic pathway indicating that the membrane environment, which is influenced by the altered sterol composition, plays an important role in the function of membrane bound proteins [42].…”

Implications ofFPS1deletion and membrane ergosterol content for glycerol efflux fromSaccharomyces cerevisiae

“…The results presented here suggest that ergosterol may play an important role in glycerol efflux and survival of S. cerevisiae yeast cells during osmotic downshock. Liposomes prepared from yeast plasma membrane lipids likewise required an adequate level of ergosterol in order to maintain membrane fluidity, which decreased with a reduction of ergosterol content [33]. The importance of ergosterol for glycerol transport has also been reported for C. albicans , where mutants inhibited in ergosterol synthesis exhibited decreased permeability for glycerol [6].…”