Abstract
Light-induced proton uptake, light-induced carotenoid absorbance shift, photophosphorylation, and hydrolysis of Mg-ATP, Ca-ATP, and PP i in Rhodospirillum rubrum chromatophores are shown to be inhibited by the antibiotic equisetin. The Mg- and Ca-ATPase activities of purified F 0F 1-ATPase are inhibited by equisetin. In contrast, only the Ca-ATPase activity of purified F 1-ATPase is decreased by equisetin, whereas the Mg-ATPase is stimulated. Both equisetin and N,N′-dicyclohexylcarbodiimide (DCCD) inhibit the hydrolytic activity of the purified H +-PPase but not the hydrolytic activity of soluble PPase from R. rubrum and yeast. The I 50 for the PP i hydrolysis is near 20 μ m for both equisetin and DCCD. The action of equisetin on membranes is compared to the effect of Triton X-100 and carbonyl cyanide p-trifluoromethoxyhydrazone. On the basis of these new data, equisetin is proposed to act nonspecifically on membranes and hydrophobic domains of proteins.
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