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Role of Galactolipids in Spinach Chloroplast Lamellar Membranes

II. Effects of Galactolipid Depletion on Phosphorylation and Electron Flow ^1,2

^a Section of Biochemistry, Molecular and Cell Biology, Cornell University, Ithaca, New York 14853

A galactolipid lipase from primary bean (Phaseolus vulgaris) leaves has been used to partially deplete spinach chloroplast inner membranes of their galactolipids. Chloroplasts treated with the lipase in the absence of bovine serum albumin lost 91% of their monogalactosyl diglyceride, 83% of their digalactosyl diglyceride, all of their phosphatidyl choline, but none of their sulfolipid. Electron microscopy of this sections revealed that the treated chloroplasts were greatly enlarged and lacked membrane stacking. Linolenic acid had similar effects on the structure of the chloroplasts. Chlorophyll, carotenoids, and coupling factor 1 remained bound to the treated membranes.

To minimize the inhibition of phosphorylation and electron flow by fatty acids released by the lipase, bovine serum albumin (15-24 mg/ml) was added to the lipase incubation mixtures. Bovine serum albumin inhibited the extent, but not the initial rate, of fatty acid release by the lipase. Electron microscopy of chloroplasts treated with the lipase in the presence of bovine serum albumin showed that membrane stacking was partially maintained. Chloroplasts treated with lipase under these conditions retained about 30% of their monogalactosyl diglyceride, 50% of their digalactosyl diglyceride and phosphatidyl choline. The sulfolipid and phosphatidyl glycerol contents were unchanged. Electron flow through photosystems I and II with artificial electron donors and acceptors was not affected by lipase treatment in the presence of bovine serum albumin. In contrast, oxygen evolution and phosphorylation were partially inhibited. These reactions are also very sensitive to fatty acids and it is possible that the inhibition is the result of interaction of fatty acids with the membrane prior to their binding to bovine serum albumin.

In view of the irreversible inactivation of electron flow and phosphorylation by fatty acids, it is difficult to assess the role of galactolipids in these processes when a specfic lipase is used to deplete the membrane.

⁴ Present address: Procter and Gamble Co., Miami Valley Laboratories, P.O. Box 39175, Cincinnati, Ohio 45239.

¹ This work was supported in part by grants GB-30597X and GB-44233X from the National Science Foundation. A.B.S. and M.M.A. were predoctoral trainees of the National Institutes of Health (5T GM-00824). Part of this work was performed when R.E.M. was a Career Development Awardee of the National Institutes of Health (GM-14,409).

² Much of the work reported here is taken from dissertations submitted by A.B.S. and by M.M.A. in partial fulfillment of the requirements for the PhD degree.