ORIENTATION OF THE PHYCOMYCES BLUE-LIGHT RECEPTOR - TESTING THE SINGLE DIPOLE HYPOTHESIS

Novel methods which combine calculated patterns of radiant energy abso rbed at the plasma membrane with the experimental tests using the vari able polarization state of the actinic light have been developed to de rive information about in situ orientation of the dichroic blue light photoreceptor in Phycomyces. The analysis of the receptor orientation has been performed within the scope of the ''single receptor and simpl e chromophore'' hypothesis which postulates that the same chromophore with a single transition dipole accounts for the light perception in b oth the lower and the higher irradiance range. This hypothesis can be retained only under the condition that the population of receptor mole cules is a mixture of non-oriented and oriented sub-populations. The o nly possible direction fur the oriented sub-population in the vicinity of lambda = 450 nm has been estimated. (C) 1997 Elsevier Science S.A.