We isolated the photoactive protein Erh, isolated from the photoreceptor of
the unicellular photosynthetic flagellate Euglena gracilis. It is a 27 kDa
protein with a photocycle resembling that of sensory rhodopsin, but with a
t least one stable intermediate. We recorded the absorption spectrum of the
parent form of this protein both under native form and in the presence of
hydroxylamine and sodium borohydride, and the fluorescence spectra of both
the parent and intermediate forms. We suggest that Erh is a rhodopsin-like
protein and propose a simple photocycle. This protein shows optical bistabi
lity, without thermal deactivation. (C) 2000 Federation of European Biochem
ical Societies. Published by Elsevier Science B.V. All rights reserved.