title: Effects of K-shell X-ray absorption of intracellular phosphorus on yeast cells.
abstract: The effects of K-shell absorption of phosphorus atoms on yeast cells were investigated using synchrotron X-rays that were tuned to the resonance absorption peak (2153 eV). Three types of cellular effect (cell inactivation, induction of gene conversion at the trp-5 locus, and cell membrane impairment (changes in the permeability] were measured. It was demonstrated that the enhancement factor was 1.4 at the resonance peak regarding both lethality and the induction of gene conversion in reference of off-peak irradiation (2146 and 2160 eV). No difference was found between the two off-peak irradiation energies. No cell membrane impairment was detected, irrespective of the X-ray photon energies employed within the fluence range tested. These results strongly suggest that K-shell X-ray absorption in the resonance mode by cellular phosphorus atoms causes significantly more cellular effects than the off-resonance mode of absorption, probably via some specific changes induced in the phosphates of the DNA strand. Calculations using the number of phosphorus atoms in a defined size of the trp locus (2127 base pairs) on the DNA and the absorption cross-section of the resonance mode of phosphorus showed that gene conversion is inducible at a rate of 0.13 per X-ray photon absorption per locus. These results are discussed regarding the modes of K-shell photoabsorption.
authors.affiliation: Institute of Biological Sciences, University of Tsukuba, Ibaraki, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Kobayashi
authors.forename: K
authors.initials: K
authors.lastname: Hieda
authors.forename: H
authors.initials: H
authors.lastname: Maezawa
authors.forename: Y
authors.initials: Y
authors.lastname: Furusawa
authors.forename: M
authors.initials: M
authors.lastname: Suzuki
authors.forename: T
authors.initials: T
authors.lastname: Ito
mesh_terms: D000042:Absorption; D002463:Cell Membrane Permeability / Q000528:radiation effects; D002470:Cell Survival / Q000528:radiation effects; D005785:Gene Conversion / Q000528:radiation effects; D010758:Phosphorus / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism / Q000528:radiation effects*
chemical_list: D010758:Phosphorus