Changes in the fluorescence of atebrin and of anilino-naphthalene sulfonate reflecting two different light-induced processes in Rhodospirillum rubrum chromatophores.

Abstract

1 The fluorescence of atebrin [3-chloro-9-(4-diethylamino-1-methyl butyl)-7-methoxyacridine] in a suspension of chromatophores was quenched in the light. This light-induced quenching was saturated at a concentration of atebrin (3 μM) which had no effect on ATP formation. The quenching was not affected by oligomycin or phosphorylation, but was completely eliminated by NH4Cl, which inhibits H+ uptake but not ATP formation in chromatophores. The inhibition by NH4Cl was not relieved by oligomycin. 2 The fluorescence of 8-anilino-naphthalene-1-sulfonate in a suspension of chromatophores, which was enhanced in the light, was affected in a completely different way by the above mentioned compounds. Thus, the addition of ADP and Pi or ADP and arsenate, strongly inhibited the light-induced enhancement in anilino-naphthalene sulfonate fluorescence. Oligomycin stimulated the rate and the extent of the enhancement in the absence of the phosphorylating reagents, and relieved the inhibition in their presence. NH4Cl had a slight stimulatory effect by itself but did not relieve the inhibition by ADP and Pi or ADP and arsenate. 3 Uncouplers which block both H+ uptake and ATP formation in the chromatophores inhibited the light-induced changes in the fluorescence of both atebrin and anilino-naphthalene sulfonate under all conditions. 4 These data indicate that the enhancement of anilino-naphthalene sulfonate fluorescence might reflect an energized state (or compound) leading to ATP formation, since ATP formation effectively competes with it and this competition is released when phosphorylation is blocked by oligomycin but not by uncouplers. On the other hand, the quenching of atebrin fluorescence is not correlated with energization leading to ATP formation, but seems rather to reflect the difference in pH between the outside and the inside of the chromatophores.