PRIMARY REACTIONS IN BACTERIAL PHOTOSYNTHESIS—I. THE NATURE OF LIGHT‐INDUCED ABSORBANCY CHANGES IN CHROMATOPHORES; EVIDENCE FOR A SPECIAL BACTERIOCHLOROPHYLL COMPONENT

Abstract

SummaryLight‐induced optical changes have been examined in chromatophores of Rhodopseudonionas spheroides (wild type and blue‐green mutants), Rhodospirillum rubrum and Chromatium. The bacteriochlorophyll (BChl) types absorbing at 850 and 870–890 mp in these chromatophores could be separated by exposure to deoxycholate, followed by differential centrifugation. By the use of this treatment and the choice of various phenotypes preparations were obtained showing great variety in the relative heights of the BChl absorption maxima at 800, 850 and 870–890 mµ.The light‐induced changes included a bleaching of the long‐wave (870–890 mk) band and blue shifts of the BChl absorption bands at 375, 590 and 800 mp. In addition, new absorption bands appeared at 420–450, 980, 1140 and 1250 mp. All these effects except the blue shift at 590 mp (and perhaps also at 375 mp) were duplicated by mild oxidation (470 mV). The interpretation is made that the loss of a ground‐state electron in BChl eliminates one optical transition (bleaching at 870–890 mp) and perturbs the energy levels of other transitions (blue shifts).The spectrum of changes induced by light or mild oxidation remains constant while the absorption spectrum varies widely from one preparation to another; it is concluded that the changes reflect alteration of a special BChl component (BChl,) comprising 2–5 per cent of the total BChl. This conclusion is reinforced by the finding, to be reported in the third paper of this series(8), that the reaction of BChl, is related kinetically to the light‐induced oxidation of a cytochrome. It is proposed that BChl, may act as an energy sink and an agent for stabilizing excitation energy in the form of separated charge.