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Effect of Inhibitors and Uncouplers on the Separate Light and Dark Reactions in Photophosphorylation

1965; Oxford University Press; Volume: 40; Issue: 6 Linguagem: Inglês

10.1104/pp.40.6.1053

1532-2548

Zippora Gromet‐Elhanan, Mordhay Avron,

Legume Nitrogen Fixing Symbiosis

The existence of a nonphosphorylated. highenergy intermediate was observed in bacterial oxidative phosphorylation, and its formation was shown to be coupled to the transport of electrons (14, 15). In chloroplasts, however, such intermediates were only postulated in the past, on the basis of analogy with the system of oxidative phosphorylation. Recently. 2 indepeln(lent groups observed such intermediates in photophosphorylation (8, 9. 16, 17). Both groups, working with chloroplasts from different sources, found these high-energy intermediates to be very unstable, with half lives of a few seconds, andl only with the development of suitable rapid techniques could their presence be ascertained (8, 16). Because of their instability, the identity of these intermediates is as yet unknown. However, with the use of the 2-stage technique adopted for the demonstration of the existence of these intermediates, the effects of various factors such as pH, temperature, light intensity and cofactors on the separate light and dark reactions were tested (8., 9, 17). With respect to these criteria the wheat seedling chloroplasts tused by the Chinese group (16. 17) behaved in a markedly different manner from the spinach chloroplasts used by Hind and jageiidorf (8, 9). In the present communication the 2-stage technique was applied to Swiss chard chloroplasts. With this system we could confirm the basic phenomenon of the formation of a very unstable, nonphosphorylated, high-energy intermediate in photophosphorylation. In most regards, the Swiss chard system reacted more like the spinach than the wheat one. By introducing a dilution of 1:20 on passing from the light to the (lark step, it became also possible to test the effect of various inhibitors and tncouplers of photophosphorylation on either the light or the dark reactions alone. In this way it was found that certain compounds affected only the light step. others only the dark reaction. Most compounds inhibited both reactions to a variable degree. Materials and Methods