Near-UV-induced absorbance change and photochemical decomposition of ergosterol in the plasma membrane of the yeast Saccharomyces cerevisiae.
When cells of the yeast Saccharomyces cerevisiae were exposed to near-UV (300-400 nm), their absorption spectra changed slightly within the range 220-300 nm with increasing dosage. Difference spectra, calculated by substracting the curve recorded in cells exposed to near-UV from the curve of unexposed cells, decreased with increasing dosage over a broad band with peaks at 272, 282 and 295 nm and a shoulder at 265 nm. These peaks were in agreement with the absorption maxima of ergosterol, which is one of the major components of the plasma membrane of yeast. Near-UV radiation induced a simultaneous decrease in absorption spectra and reduction of ergosterol content in the plasma membrane. Photochemical decomposition of ergosterol by near-UV radiation was revealed in vivo, although ergosterol is generally known to be photoconverted to previtamin D2 industrially by UV radiation in vitro. In order to remove photosensitizers, liposomes were prepared from phospholipids and glycolipids, with or without ergosterol from purified yeast plasma membranes. Liposomal ergosterol in the orientated state was photochemically decomposed by near-UV radiation but ergosterol in the disorientated state in a homogeneous solution was not. Near-UV radiation also induced a decrease in activity of membrane-bound ATPase. Dose-response curves for the reduction of ATPase activity were similar to that for decomposition of ergosterol, suggesting that near-UV caused membrane function damage.
Arami
Shin-Ichiro
SI
Division of Biological Function and Genetic Resources Science, Faculty of Agriculture, Okayama University, Tsushima-naka, Okayama 700, Japan.
Hada
Megumi
M
Department of Biology, Kobe University, Rokkodai, Nada-ku, 657 Kobe, Japan.
Tada
Mikiro
M
Division of Biological Function and Genetic Resources Science, Faculty of Agriculture, Okayama University, Tsushima-naka, Okayama 700, Japan.
D000251:Adenosine Triphosphatases / Q000378:metabolism; D002462:Cell Membrane / Q000528:radiation effects; D004307:Dose-Response Relationship, Radiation; D004875:Ergosterol / Q000528:radiation effects*; D005656:Fungal Proteins / Q000378:metabolism; D008081:Liposomes / Q000528:radiation effects; D008563:Membrane Lipids / Q000528:radiation effects*; D010777:Photochemistry; D012441:Saccharomyces cerevisiae / Q000737:chemistry / Q000528:radiation effects*; D013056:Spectrophotometry, Ultraviolet; D014466:Ultraviolet Rays
D005656:Fungal Proteins; D008081:Liposomes; D008563:Membrane Lipids; D000251:Adenosine Triphosphatases; D004875:Ergosterol