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A preparation of purified Rhodospirillum rubrumphotoreaction centres was subjected to dialysis under mild denaturing conditions. Sodium dodecyl sulfate—polyacrylamide gel electrophoresis showed that the resulting prepartation contained only one peptidic constituent, apparently the lighter one. The dialyzed centres retained the characteristic absorption spectrum in the visible—near infrared range and actinic light elicited the spectral changes which reflect primary change separation. Thus, it seems that the light protein of the photoreaction centre contains all the binding sites for the primary reactants of bacterial photosynthesis.

A preparation of purified Rhodospirillum rubrumphotoreaction centres was subjected to dialysis under mild denaturing conditions. Sodium dodecyl sulfate—polyacrylamide gel electrophoresis showed that the resulting prepartation contained only one peptidic constituent, apparently the lighter one. The dialyzed centres retained the characteristic absorption spectrum in the visible—near infrared range and actinic light elicited the spectral changes which reflect primary change separation. Thus, it seems that the light protein of the photoreaction centre contains all the binding sites for the primary reactants of bacterial photosynthesis.

Photoreaction centers were purified from wild‐type Rhodospirillum rubrumby a new procedure which reduced to undetectable levels the activities of contaminant endogenous proteinases. As shown by sodium dodecylsulfate‐polyacrylamide gel electrophoresis, mild digestion of the centers with α‐chymotrypsin degraded the 36 kDa (H) polypeptide but did not elicit significant alterations in the 29 (M) and 25 kDa (L) constituents. While short‐term incubation with trypsin removed H and decreased the Mrof M to that of L, a prolonged treatment with trypsin yielded preparations with polypeptides of 19 and 5 kDa. Since the proteolyzed preparations retained the near infrared absorption spectrum of the native photoreaction center and exhibited photochemical activity, an apparent 3–4‐fold increase of the primary donor:protein ratio was achieved.

Photoreaction centers were purified from wild-type Rhodospirillum rubrumby a new procedure which reduced to undetectable levels the activities of contaminant endogenous proteinases. As shown by sodium dodecylsulfate-polyacrylamide gel electrophoresis, mild digestion of the centers with α-chymotrypsin degraded the 36 kDa (H) polypeptide but did not elicit significant alterations in the 29 (M) and 25 kDa (L) constituents. While short-term incubation with trypsin removed H and decreased the Mrof M to that of L, a prolonged treatment with trypsin yielded preparations with polypeptides of 19 and 5 kDa. Since the proteolyzed preparations retained the near infrared absorption spectrum of the native photoreaction center and exhibited photochemical activity, an apparent 3–4-fold increase of the primary donor:protein ratio was achieved.