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 lmol m −2 s −1 (total fluence of 1200 lmol 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.

Chloroform‐extractable green fraction (CEGF) was detected in the supernatant obtained by alkali precipitation from the HCI‐dimethylsulfoxide (DMSO) extract of Pg‐rich soil. In the alkaline solution, the color of CEGF was green and CEGF showed strong Pg‐like absorption bands. Ultraviolet and visible (UV‐VIS) spectral analysis and gel chromatography on Sephadex G‐50 were performed to compare several properties between CEGF and Pg. CEGF, which was purified by gel chromatography on Bio‐Beads SX‐1, displayed strong absorption bands at 609, 562, 445 and 280 inn in the alkaline solution. These absorption bands were almost similar to those of Pg. Furthermore, the UV‐VIS spectrum of CEGF in the organic solvents showed a similar characteristic pattern of 4,9‐dihydroxyperylene‐3,10‐quinone (DHPQ), which was considered to be a chromophore of Pg. Based on the results of gel chromatography on Sephadex G‐50, CEGF mainly consisted of two fractions, corresponding to the G2 and G3 fractions of Pg. These results indicated that the method for extracting CEGF from Pg‐rich soil in the present study was easy and selective and that CEGF was one of the components of, or a closely related substance to Pg. A colorimetric method for the estimation of the CEGF content in soils was developed. The calibration curve of CEGF was linear over a wide range of contents from 2.75 to 220 mg L−1. The CEGF content in twelve samples of various soils was examined. CEGF was detected in all the soil sampled (5 orders) including three samples (3 orders) where Pg was not detected, and the content ranged from 0.07 to 1.66 g kg−1 (dry soil). Therefore, the method for estimating the CEGF content in soils developed in the present study was found to be suitable for various soil orders and it was assumed that CEGF occurred in various soil orders.

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