Synthesis, Structure, and Properties of MeSer1-Tentoxin, a New Cyclic Tetrapeptide Which Interacts Specifically with Chloroplast F1H+-ATPase Differentiation of Inhibitory and Stimulating Effects

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Abstract
A new tentoxin analogue, in which the l-methyl alanine residue is substituted by l-methylserine, has been prepared following the synthetic pathway recently described for the synthesis of tentoxin [Cavelier, F., & Verducci, J. (1995) Tetrahedron Lett.36, 4425−4428]. Using two-dimensional homonuclear proton nuclear magnetic resonance and structural analysis, we observed that MeSer1-tentoxin, like tentoxin, adopts several conformations in aqueous solution and presents self-aggregative properties. This analogue was found to be conformationally similar to the natural toxin. It showed the same efficiency as tentoxin in inhibition of ATPase activity of the isolated chloroplast F1 proton ATPase (CF1) as well as in inhibition of the ATP synthase activity of the membrane-bound enzyme (CF0CF1) in thylakoids and proteoliposomes. At concentrations above 10 μM, MeSer1-tentoxin did not reactivate CF1 to a high extent, contrary to tentoxin. It appeared, however, to bind in the same way, since the reactivating effect of tentoxin was inhibited by MeSer1-tentoxin. These results show that it is possible, using tentoxin analogues, to separate inhibitory and activating effects on the chloroplast ATPase, despite the limited chemical difference between the two toxins.