Fatty acid synthesis by spinach chloroplasts, 3

The modes of actions of photosynthetic inhibitors on photosynthesis and fatty acid synthesis were examined. DCMU, an electron transport inhibitor, inhibited fatty acid synthesis and photophosphorylation to the same extent, suggesting dependence of fatty acid synthesis on photosynthesis. The same was also the case with FCCP, a photophosphorylation uncoupler. In contrast, NH4Cl and phlorizin at concentrations completely suppressing ATP formation, only partially inhibited the fatty acid synthesis. These facts suggest that a certain level of high-energy intermediate (state) is responsible for the light enhancement of fatty acid synthesis. This idea is further supported by the fact that the partial inhibition of fatty acid synthesis by NH4Cl was relieved by addition of DCCD at low concentrations suppressing the ATP formation but not completely destroying the high energy intermediate. The lag period in the initial period of fatty acid synthesis was shortened by preillumination of chloroplasts, even in the absence of ADP. This indicates that the light dependent fatty acid synthesis is closely associated with the high-energy intermediate (state), but not directly with ATP formation by photophosphorylation. (author)