IN-VIVO PHOTOCYCLE OF THE EUGLENA-GRACILIS PHOTORECEPTOR

We present the light-induced photocycle of the paraflagellar swelling of Euglena gracilis. The kinetics of this process was reconstructed by sampling its fluorescence emission and switching the excitation light from 365 nm to 436 nm. Stable intermediates in the photocycle were ma nifested. The measured millisecond resolution kinetics best fits a Mic haelis-Menten equation. The data provide strong evidence that the para flagellar swelling, a three-dimensional natural crystal of a light-det ecting protein, is the true Euglena photoreceptor.