. Biological structure and function; proceedings. Biochemistry; Cytology. PHOTOSYNTHETIC MACROMOLECULES OF CHLOROBIUM THIOSULFATOPHILUM 319 rods. This tendency of the macromolecules to organize into structures with a higher degree of order than is observed in the organism is unusual. In the initial phase of this study, observations on the chemical composi- tion of the pigmented fractions have dealt primarily with chlorophyll, protein and nucleic acids. The spectrophotometric assay of chlorophyll content is based on the specific absorption coefficient of this chlorophyll in acetone [37] and a r
. Biological structure and function; proceedings. Biochemistry; Cytology. PHOTOSYNTHETIC MACROMOLECULES OF CHLOROBIUM THIOSULFATOPHILUM 319 rods. This tendency of the macromolecules to organize into structures with a higher degree of order than is observed in the organism is unusual. In the initial phase of this study, observations on the chemical composi- tion of the pigmented fractions have dealt primarily with chlorophyll, protein and nucleic acids. The spectrophotometric assay of chlorophyll content is based on the specific absorption coefficient of this chlorophyll in acetone [37] and a recent estimate of the molecular extinction coefficient [14]. The quantitative relationship between the 723 m/x maximum in the in vivo spectrum and the 652 m/z maximum of the chlorophyll in acetone has been determined in order to allow direct measurement of chlorophyll Q300 0200 1 M I I M I I [ I I I I I I I i T I I M ; I 1 I i I ] M I I I I I M I -EXTRACTED IN HjS SATURATED ACETONE, m^ ON BEARER IN M TRIS, pH 78, m^ M I I I I I M. CONCENTRATION Fig. io. Quantitative determination of the relationship of the absorption at 652 ni/tt of the chlorophyll in H.^S-saturated acetone and the absorption at 723-5 m^ of the chlorophyll bound to the pigmented particle. content in the extract during fractionation (Figs. lo and ii). For the same reason the nucleic acid and protein estimates have been limited to ultra- violet absorption measurements. During the course of fractionation the absorption maximum at 260 m^u decreases from an initial value w^hich is two or three times greater than the chlorophyll maximum at 723 m/x to a limiting value which is 13 of the chlorophyll absorption. The initial 280/ 260 m/i absorption ratio is about 0-5 and increases to 0-9; thus, the 50 S fraction is quite free of nucleic acids. On a mass basis, the chlorophyll/ protein ratio in the more highly purified preparations is 1/13. Assuming that these two components acco
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