TRIPHENYLTIN AS AN INHIBITOR OF MEMBRANE-BOUND PYROPHOSPHATASE OF RHODOSPIRILLUM-RUBRUM

The effect of triphenyltin on the activity of membrane-bound pyrophosp hatase of Rhodospirillum rubrum was investigated. Triphenyltin inhibit s the hydrolysis of chromatophore membrane-bound pyrophosphatase in a pH-dependent pattern, being maximal at pH 9-10. At basic pH values, th e inhibition produced by this organotin on membrane-bound pyrophosphat ase is very similar to that produced on the chromatrophore H+ ATPase ( I-50 = 14.4 and 10 mu M, respectively). Detergent-solubilized membrane -bound pyrophosphatase is also inhibited by triphenyltin, but the cyto plasmic 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 V-max of the enzyme, a nd only slightly its K-m. Free Mg2+ does not reverse the inhibition. R educing agents prevent triphenyltin inhibition of the membrane-bound p yrophosphatase, but their effect is due to an alteration of the inhibi tor, and not to a modification of thiol groups of the enzyme. The most likely site for triphenyltin inhibition in chromatophore membrane-bou nd pyrophosphatase is a component either within or closely associated with the membrane. (C) 1998 Academic Press.