Triphenyltin as an inhibitor of membrane-bound pyrophosphatase of Rhodospirillum rubrum.
The effect of triphenyltin on the activity of membrane-bound pyrophosphatase of Rhodospirillum rubrum was investigated. Triphenyltin inhibits the hydrolysis of chromatophore membrane-bound pyrophosphatase in a pH-dependent pattern, being maximal at pH 9-10. At basic pH values, the inhibition produced by this organotin on membrane-bound pyrophosphatase is very similar to that produced on the chromatophore H+ATPase (I50 = 14.4 and 10 microM, respectively). Detergent-solubilized membrane-bound pyrophosphatase is also inhibited by triphenyltin, but the cytoplasmic enzyme of R. rubrum is inhibited only slightly. The inhibitory effect of triphenyltin on membrane-bound pyrophosphatase is the same with Mg-PPi or Zn-PPi, and is dependent on the chromatophore membrane concentration. Triphenyltin modified mainly the Vmax of the enzyme, and only slightly its Km. Free Mg2+ does not reverse the inhibition. Reducing agents prevent triphenyltin inhibition of the membrane-bound pyrophosphatase, but their effect is due to an alteration of the inhibitor, and not to a modification of thiol groups of the enzyme. The most likely site for triphenyltin inhibition in chromatophore membrane-bound pyrophosphatase is a component either within or closely associated with the membrane.
Celis
H
H
Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, México, 04510, D. F. México. hcelis@ifcsun1.ifisiol.unam.mx
Escobedo
S
S
Romero
I
I
D004024:Dicyclohexylcarbodiimide / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D006868:Hydrolysis / Q000187:drug effects; D008565:Membrane Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism*; D009947:Organotin Compounds / Q000494:pharmacology*; D011755:Pyrophosphatases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D012247:Rhodospirillum rubrum / Q000187:drug effects / Q000201:enzymology*; D012995:Solubility; D013438:Sulfhydryl Compounds / Q000494:pharmacology
D008565:Membrane Proteins; D009947:Organotin Compounds; D013438:Sulfhydryl Compounds; D004024:Dicyclohexylcarbodiimide; C030665:triphenyltin; D011755:Pyrophosphatases; C067974:membrane-bound proton-translocating PPi synthase