Lipids of mitochondria

The properties of a discrete membranous fraction isolated on sucrose gradients from castor bean endosperm have been examined. This fraction was previously shown to be the exclusive site of phosphorylcholine-glyceride transferase. The distribution of NADPH-cytochrome c reductase and antimycin insensitive NADH-cytochrome c reductase across the gradient followed closely that of the phosphorylcholine-glyceride transferase. This fraction also had NADH diaphorase activity and contained cytochromes b5 and P 450. On sucrose gradients containing 1 mM EDTA this fraction had a mean isopycnic density of 1.12 g/cm3 and sedimented separately from the ribosomes; electron micrographs showed that it was comprised of smooth membranes. When magnesium was included in the gradients to prevent the dissociation of membrane-bound ribosomes, the isopycnic density of the membrane fraction with its associated enzymes was increased to 1.16 g/cm3 and under these conditions the electron micrographs showed that the membranes had the typical appearance of rough endoplasmic reticulum. Together these data show that the endoplasmic reticulum is the exclusive site of lecithin formation in the castor bean endosperm and establish a central role for this cytoplasmic component in the biogenesis of cell membranes.

/pdf/endoplasmic-reticulum-as-the-site-of-lecithin-formation-in-52nrlitprn.pdf

Endoplasmic reticulum as the site of lecithin formation in castor bean endosperm

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

Plastid differentiation, acyl lipid, and fatty acid composition have been followed in successive 2-cm sections from the base (youngest tissue) to the tip (oldest tissue) of green Zea mays (maize) leaves grown under a normal diurnal light regime. Although the youngest cells (0-4 cm from the leaf base) had only proplastids with one or two grana, they contained chlorophylls a and b, monogalactosyldiglyceride, digalactosyldiglyceride, sulfolipid, phosphatidylcholine, phosphatidylethanolamine, and phosphatidylglycerol. In the more mature sections, the plastids increased in size 5-fold, and differentiation into mesophyll and bundle-shealth chloroplasts had occurred. Concomitantly, the levels of all the lipids increased with the exception of phosphatidylcholine and phosphatidylethanolamine which decreased. With increasing cell maturity, the percentage of linolenic acid increased in all the individual acyl lipids, but palmitic acid remained constant in phosphatidylcholine, phosphatidylethanolamine, and sulfolipid. The Δ3t-hexadecenoic acid was only detectable in the phosphatidylglycerol of the most mature maize tissue.

K.A. Devor

Papers

Biosynthesis of phosphatidylcholine by enzyme preparations from spinach leaves

Structural analysis of phosphatidylcholine of plant tissue.

Control of fatty acid distribution in phosphatidylcholine of spinach leaves