https://deepblue.lib.umich.edu/bitstream/2027.42/30145/1/0000522.pdf

Cardiolipins and biomembrane function

Publisher Summary This chapter describes the composition and cellular distribution of plant phospholipids and glycolipids and their cellular metabolism. Early studies on the lipids of plants had revealed only the presence of components well known in animal tissues, namely, phosphatidylcholine (lecithin), phosphatidylethanolamine and phosphatidylserine (cephalins), and phosphatidylinositol. Phosphatidic acid had been isolated from plant tissue and was considered to be a characteristic plant phosphatide, but this component was subsequently shown to be largely an artifact formed by enzymatic degradation during extraction of the lipids. Distribution of unsaturated fatty acids among the phospholipid and glycolipid components of both photosynthetic and nonphotosynthetic tissues is by no means uniform. In general, the galactolipids have very high contents of linolenic and C16 -trienoic acids in photosynthetic tissues grown in the light, or linoleic acid in nonphotosynthetic tissues. Phospholipids and glycolipids exist in a dynamic state of equilibrium in the membrane structures of plant cells, as may be readily demonstrated in studies using radioisotopes. Rapid incorporation of radioisotopes observed when plants cells are exposed to labeled presursors such as phosphate- 32P or 14CO2 is the result of a steady-state cycle of degradative and synthesizing reactions.

Plant Phospholipids and Glycolipids

Fat metabolism in higher plants

Publisher Summary In higher plants, the process of photosynthesis occurs within specific membrane bounded organelles called “chloroplasts.” All the chloroplasts exhibit three major structural regions— namely, highly organized internal sac-like flat compressed vesicles called “thylakoids,” an amorphous background rich in soluble proteins called “stroma,” and a pair of outer membranes known as the “envelope.” The envelope essentially renders functional and structural integrity to the chloroplast. This chapter discusses the structure, isolation, chemical composition, and origin of the higher plant chloroplast envelope. The chapter examines the multiple functions of this important membranous system involved in the regulation of the inflow of raw materials for photosynthesis and the outflow of photosynthetic products. The chloroplast envelope of higher plants is a permanent structure and consists of two morphologically and topologically distinct membranes separated by a region about 10–20 nm thick, which appears electron-translucent. The structure of both envelope membranes is consistent with the lipid-globular protein mosaic model of membrane structure as proposed by Singer and Nicolson.

Structure and Function of the Plastid Envelope

Plant lipids and their role in membrane function.

Biosynthesis of galactolipids by enzyme preparations from spinach leaves.

A method is described for the isolation of subcellular membranes of Entamoeba invadens. Plasma membranes were obtained by rate centrifugation followed by isopycnic centrifugation on a sucrose gradient. Intact phagolysosomes floated in a 10% sucrose solution providing a simple technique for isolation. Phagolysosomal membranes were collected by isopycnic centrifugation, after lysis of the phagolysosomes. Microsomes were obtained by differential centrifugation. Membrane fractions were examined by electron microscopy, and the contamination of each fraction was determined with marker enzymes. Mg2+-ATPase is associated with the plasma membrane. Acid phosphatase (beta-glycerophosphate) was associated mainly with phagolysosmal membranes. Plasma membranes also contained acid phosphatase activity which hydrolyzes p-nitrophenylphosphate but not beta-glycerophosphate. The localization of the two phosphatases was confirmed cytochemically. Isolated plasma membranes were contaminated with phagolysosomal membranes (15%) and with microsomes (25%). No more than 5% of the phagolysosomal membrane fraction consisted of plasma membranes. Contamination of the microsomes by plasma and phagolysosomal membranes was 10% and 7%, respectively. Plasma membranes and phagolysosomal membranes had a high ratio of cholesterol to phospholipid (0.93 and 1.05 mumol/mumol, respectively). Microsomes were relatively poor in cholesterol (0.39 mumol/mumol). Microsomes, plasma, and phagolysosomal membranes contained increasing amounts of spingolipids (12%, 17%, and 28%). Phagolysosomal membranes had a high percentage of phosphatidylserine but little phosphatidylcholine. Microsomes were rich in phosphatidylcholine (45%). Differences in phospholipid composition between plasma and phagolysosomal membranes are discussed in view of the phagocytic process.

https://rupress.org/jcb/article-pdf/71/2/357/1387680/357.pdf

H.H.D.M. van Vliet

Papers

Biosynthesis of galactolipids by enzyme preparations from spinach leaves.

Isolation and characterization of subcellular membranes of Entamoeba invadens.

Phospholipids of Entamoeba invadens