Abstract
Organelle membranes subfractionated from nodules of Glycine max differed in lipid composition. Of the enzymes assembling phospholipids, choline kinase (EC 2.7.1.32) was recovered in the cytoplasmic fraction whereas CDP choline 1,2-diacylglyceride choline phosphotransferase (EC2.7.8.2) was located in the ER. When methyl [14C]CDP choline was supplied to nodules in vivo radioactivity was found in the ER. On longer labelling periods [14C]phosphatidylcholine spread into denser regions of the gradient, including the peribacteroid membrane (which surrounds the Rhizobium japonicum symbiont). [14C]Phosphatidylcholine was a notable component of such membranes. Adenosine triphosphatase (EC 3.6.1.3) activity in the peribacteroid membrane fraction was compared to that of other major organelle fractions. The peribacteroid membrane ATPase was equally active on pH 6.0 and 8.0, was stimulated by K+ and inhibited by DES, DCCD and MoO4. In these respects it was more similar to the ATPase activity in the ER and mitochondria than in tonoplast or cytoplasm. The results are discussed in relation to modes of peribacteroid membrane biogenesis, including enzyme modification.
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