Irwin D. Kuntz

KINETIC STUDIES OF THE TWO LIGHT REACTIONS IN PHOTOSYNTHESIS

Abstract— The decay kinetics of the photo‐induced absorbance changes in red and green algae are very sensitive to the wavelength of the actinic light. A four to tenfold increase in half‐decay time is noted in going from short wavelength (550–650 mμ) to long wavelength (> 700 mμ) excitation. The slow decay rates produced by long wavelength light can be enhanced with a steady background of short wavelength light. A relationship between initial decay rates and O2 evolution rates is described. This relationship allows a direct correspondence between these spectroscopic studies and the ‘red‐drop’ and ‘enhancement’ experiments of Emerson.

ABSORPTION CHANGES IN BACTERIAL CHROMATOPHORES‐II. A NEW CHLOROPHYLL‐LIKE PIGMENT FROM THE OXIDATION OF CHROMATQPHORES FROM RHODOSPIRILLUM RUBRUM

Abstract— Evidence is presented which points to (at least) two bound forms of bacteriochlor‐ophyll present in chromatophores of Rhodospirillum rubrum, both of them readily converted to unbound bacteriochlorophyll (abs. max 770 mμ) when the chromatophores are extracted with acetone or ethanol. Controlled oxidation of the chromatophores with Ir(IV) or with Zn (II) and ferricyanide preferentially destroys the more strongly absorbing pigment (abs. max 880 mμ) but brings about only a slight decrease in the magnitude of the photoinduced absorption changes at 810 and 792 mμ. Such oxidations yield a new pigment, absorbing at 715 mμ in the aqueous preparation and, more strongly, at 680–684 mu when the pigment is extracted into organic solvents. This pigment is formed irreversibly and is therefore different from the material formed by photooxidation of chromatophores. Its visible spectrum and the spectrum of the material formed from it by acidification suggest that it is a chlorophyll‐like substance, possibly derived from bacteriochlorophyll by (two‐electron) oxidation of one of the dihydropyrrole rings to a pyrrole ring. Directions are given for separation of this pigment from other colored compounds present in the oxidation mixtures.