Photoreaction center of photosynthetic bacteria. 1. Further chemical characterization of the photoreaction center from Rhodospirillum rubrum

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Abstract
The photoreaction center from R. rubrum contains about 90% protein, 6% pigment, traces of lipids, and no cytochromes. It also contains at least 1 mol of ubiquinore and 1 Fe atom/mol. Its 3-component polypeptide chains were isolated by preparative electrophoresis, and their molar stoichiometry was established as 1:1:1. The amino acid composition of the photoreaction center from strain S1 and from its subunits is reported. The protein as a whole contains about 65% nonpolar residue, and the degree of hydrophobicity of its subunits is .alpha. < .beta. < .gamma.. The minimal MW based on the extinction coefficient and on the amino acid content is 90,000. This corresponds to a half-cystine mole number of 6.