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Cells from serial cultures of R. rubrum, grown anaerobically in the light, were harvested at intervals from ~/~ to 15 days and sectioned for electron microscopy by conventional methods.Cells of this species possess a multilayered outer envelope, and the external cell surface is differentiated into ridges extending parallel or obliquely to the long axis of the cell.Cells from very young cultures resemble non-photosynthetic bacteria and contain only a granular cytoplasm, scattered high-density particles, and lowdensity areas corresponding to the chromatin areas observed by light microscopy. They contain neither the chromatophores nor the lame]lar systems assumed by previous investigators to be characteristic of this species when grown anaerobically in the light.Chromatophores appear in cells from cultures older than about 12 hours, while systems of paired lamellae appear along with the chromatophores in cells from cultures older than about 8 days. Divergent opinions concerning the occurrence of chromatophores or lamellae in this species can be resolved on the basis of the age of cultures used in previous studies.Other changes occurring in ceils from cultures of increasing age include the appearance of granular and reticulate cytoplasmic bodies and vacuoles, extension of the chromatin areas, and the appearance of a single membrane enclosing several chromatophores.

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The lamellae of the bacterium Rhodospirillum molischianum originate as extensions of the cytoplasmic membrane into the cytoplasm of the cell. Initially, these extensions arc narrow folds and occur independently of one another. The first lamellae to appear average about 80 A in width, representing one side of the infolded cytoplasmic membrane, or 160 A when the two sides of the fold are closely apprcssed. The 160-A lamellae increase in number and may associate to form larger lamellae, which represent varying degrees of association between adjacent folds. Later, the space within each fold increases; the two appresscd regions of the cytoplasmic membrane in each fold separate to form distinct invaginations, and the lamellae observed at this stage are formed by an association of the sides of adjacent invaginations.

Abstract— The photooxidation of epinephrine, sensitized by methylene blue or by chlorophylls, excited with red light, involves the reduction of two molecules of oxygen to hydrogen peroxide per molecule of epinephrine oxidized to adrenochrome. The initial rates of these reactions are not affected by low concentrations of catalase. In 99 mol % D2O, rates of methylene blue sensitized photooxidations are accelerated as much as 5.2 times over rates in ordinary water. Azide anion is a more effective inhibitor of this reaction in D2O than in H2O. Half maximal inhibitions are obtained by 1.3 mM azide in H2O and by 0.1 mAf azide in D2O. Isotope effects and azide sensitivities point to photooxidation of epinephrine in D2O primarily by a singlet oxygen pathway; in H2O, non‐singlet oxygen pathways become more predominant. Superoxide dismutase (SOD) markedly inhibits rates of the photooxidations in H2O and in D2O; about 25% at 10‐9M SOD, and 50% at 10‐6M SOD in H2O. In the photooxidation in H2O, both by non‐singlet and singlet oxygen mechanisms, the amount of superoxide produced is equivalent to the amount of O2 consumed in the photooxidation of epinephrine; the superoxide thus formed participates in the oxidation of epinephrine.