Light-induced absorbance changes in Phycomyces: evidence for cryptochrome-associated flavosemiquinones.
Light-induced absorbance changes (LIACs), which are associated with early photochemical events of blue-light transduction, were detected in growing zones of Phycomyces sporangiophores. The novel LIACs meet all the essential requirements for a spectrophotometric photoreceptor assay which was previously unavailable for blue-light receptors (cryptochromes). In-vivo absorption spectra of growing zones were derived from reflection spectra which were measured with a novel rapid-scan spectrophotometer. To detect photoreceptor-associated absorbance changes white mutants were employed which lack the interfering bulk pigment beta-carotene. Blue and white light, not however red light, induced in these strains absorbance changes near 460-490 and 600-620 nm. The LIACs were absent in light-insensitive mutants with defects in the genes madA, madB and madC. Because these genes affect photosensory adaptation and the blue-light receptor itself, the novel in-vivo LIACs must be associated with photochemical events which occur early in the transduction chain. The spectral characteristics of the LIACs are in accordance with a blue- and red-light absorbing flavosemiquinone which is generated upon light absorption by an oxidized flavin receptor. It is proposed that the flavosemiquinone functions itself as photoreceptor which mediates several red-light responses of Phycomyces.
Schmidt
W
W
Fachbereich Biologie/Botanik, Philipps-Universität, Marburg, Germany.
Galland
P
P
D056931:Cryptochromes; D029721:Drosophila Proteins; D005136:Eye Proteins; D005420:Flavoproteins / Q000378:metabolism*; D008027:Light; D017956:Photoreceptor Cells, Invertebrate; D010800:Phycomyces / Q000378:metabolism*; D011809:Quinones / Q000378:metabolism*; D043562:Receptors, G-Protein-Coupled; D013053:Spectrophotometry
D056931:Cryptochromes; D029721:Drosophila Proteins; D005136:Eye Proteins; D005420:Flavoproteins; D011809:Quinones; D043562:Receptors, G-Protein-Coupled; C119828:cry protein, Drosophila; C001636:flavosemiquinone