RRC ID 20352
Author Yoshikawa S, Suzuki T, Watanabe M, Iseki M.
Title Kinetic analysis of the activation of photoactivated adenylyl cyclase (PAC), a blue-light receptor for photomovements of Euglena.
Journal Photochem Photobiol Sci
Abstract Photoactivated adenylyl cyclase (PAC) was first purified from a photosensing organelle (the paraflagellar body) of the unicellular flagellate Euglena gracilis, and is regarded as the photoreceptor for the step-up photophobic response. Here, we report the kinetic properties of photoactivation of PAC and a change in intracellular cAMP levels upon blue light irradiation. Activation of PAC was dependent both on photon fluence rate and duration of irradiation, between which reciprocity held well in the range of 2--50 micromol m(-2) s(-1)(total fluence of 1200 micromol m(-2)). Intermittent irradiation also caused activation of PAC in a photon fluence-dependent manner irrespective of cycle periods. Wavelength dependency of PAC activation showed prominent peaks in the UV-B/C, UV-A and blue regions of the spectrum. The time course of the changes in intracellular cAMP levels corresponded well with that of the step-up photophobic response. From this and the kinetic properties of PAC photoactivation, we concluded that an increase in intracellular cAMP levels evoked by photoactivation of PAC is a key event of the step-up photophobic response.
Volume 4(9)
Pages 727-31
Published 2005-9-1
DOI 10.1039/b417212d
PMID 16121284
MeSH Adenylyl Cyclases / chemistry Adenylyl Cyclases / metabolism* Animals Cyclic AMP / metabolism Euglena gracilis / enzymology* Kinetics Light Photoreceptor Cells, Invertebrate / chemistry Photoreceptor Cells, Invertebrate / metabolism* Time Factors
IF 2.831
Times Cited 31
Algae NIES-48