Membrane biosynthesis

Bishop, W.R. Bell, R.M. (1988) Assembly of phospholipids into cellular membranes biosynthesis, transmembrane movement and intracellular translocation. Ararat. Rev. Cell Biol. 4, 579-610. Advanced review of the enzymology and cell biology of phospholipid synthesis and targeting. 

In bacterial lipopolysaccharides, O-specific chains composed of repeating, or modified repeating, units are linked to a unique oligosaccharide sequence of the core region which is connected to a lipid A fragment serving as a hydrophobic anchor embedded in the bacterial outer-membrane. Biosynthesis of O-specific chains was found to occur independently on formation of other structural fragments of the lipopolysaccharide molecule. Both block and monomeric mechanisms were demonstrated for the biosynthesis of these polymers. 

It has been determined that the PBM comprises approximately 20 times more membrane than the plasma membrane (Verma et al., 1978). Therefore, massive membrane biosynthesis is required during the course of PBM formation. However, it is not clear what signals are responsible for this highly regulated membrane biosynthesis in the developing nodules. One of the key enzymes in the phospholipid biosynthetic pathway has been shown to be induced in soybean nodules and has been suggested to be a nodulin (Mellor et al., 1986). 

Lykidis A and Jackowski S (2001) Regulation of mammalian cell membrane biosynthesis. Progress in Nucleic Acid Research and Molecular Biology 65,361-93. 

The released unesterified cholesterol can then be usedfor membrane biosynthesis. Alternatively, it can be reesterified for storage inside the cell. In fact, free cholesterol activates acyl CoA cholesterol acyltransferase (ACAT), the enzyme catalyzing this reaction. Reesterified cholesterol contains mainly oleate and palmitoleate, which are monounsaturated fatty acids, in contrast with the cholesterol esters in LDL, which are rich in linoleate, a polyunsaturated fatty acid (see Table 24.1). It is imperative that the cholesterol be reesterified. High concentrations of unesterified cholesterol disrupt the integrity of cell membranes. 

A. Lykidis and S. Jackowski. 2000. Regulation of mammalian cell membrane biosynthesis Prog. Nucleic Acid Res. Mol. Biol. 65 361-393. (PubMed)... 

The supply of lipids for mitochondrial membrane biosynthesis depends largely on lipids synthesized elsewhere in the cell, especially the endoplasmic reticulum. However, one major lipid component of the inner mitochondrial membrane, cardiolipin (diphosphatidylglycerol), is synthesized within the mitochondria. 

Because of the potentially great heuristic value of knowledge about membrane structure, the following three sections are devoted to a summary of the repeating unit concept as it appears most relevant to the study of receptor systems. Mention is made of the molecular nature of the repeating units, the types of cohesive and repulsive forces that appear to be important in membrane systems, and discernible relationships between form and function. The probable mode of membrane biosynthesis is reviewed as a likely source of fundamental insights. 

The question of membrane biosynthesis and its regulation is controversial. It is known that virtually all of the proteins that eventually are incorporated into the cell membrane are synthesized at the rough endoplasmic reticulum. These proteins and the complex lipids destined for the cell membrane are often further modified at the Golgi apparatus, where postribosomal glycosy-lation of proteins is known to occur and where many complex membrane-associated lipids are processed. An understanding of the mechanisms that... 

The measurement of fluorescence redistribution after photobleaching (FRAP) is a unique, noninvasive method for direedy analyzing dynamic processes in living cells (13, 18-23, 69-73). FRAP experiments have provided important insights into membrane structure (18, 20), mechanisms of hormone action (82, 83), nucleocytoplasmic communication (13, 21), cytoplasmic organization and structure (84), actin and tubulin assembly (85, 22), cell-cell communication (13, 65, 67-69), cell differentiation and proliferation (86), parasite membrane structure (87), and bacterial membrane biosynthesis (88-89). 

A fundamental principle of membrane biosynthesis is that cells synthesize new membranes only by the expansion of existing membranes. Although some early steps in the synthesis of membrane lipids take place in the cytoplasm, the final steps are catalyzed by enzymes bound to preexisting cellular membranes, and the products are incorporated into the membranes as they are generated. Evidence for this phenomenon is seen when cells are briefly exposed to radioactive precursors... 

Kiley, P.J., and Kaplan, S. (1988) Molecular genetics of photosynthetic membrane biosynthesis in Rhodobacter sphaeroides. Microbiol. Rev. 52, 50-69. 

Maragoudakis, M. E., Sarmonika, M., and Panoutscaopoulou, N. (1988) Inhibition of basement membrane biosynthesis prevents angiogenesis. J. Pharmacol Exp. Therapy 244,729-733. 

Up to the levei of protoporphyrin IX, C. biosynthesis is the same as that of the Porphyrins (see), bearing in mind that different mechanisms exist for the biosynthesis of S-aminolevulinate, depending on the organism. Conversion of protoporphyrin IX into Cm is shown in Fig. 3. The final steps of biosynthesis appear to take place in situ in the thylakoid membrane. [Biosynthesis of Heme and Chlorophylls, H. A. Dailey (ed.) McGraw Hill, 1990 S.B. Brown etal. J. Photo-chertu Photobiol., B Biology S (1990) 3-23]... 

Schizosaccharomyces, and Zygosaccharomyces require at least 2 mg/L molecular SOg for inhibition (Warth, 1985), a difficult concentration to obtain given that the presence of molecular SOg depends highly on pH (Fig. 5.1). Mechanisms of SO2 resistance differ but are related to variable rates of diffusion across cell membranes, biosynthesis of compounds that bind SO2, and varying enzyme sensitivity (Romano and Suzzi, 1993). 

More recently, Baron and Abrams (1971) isolated a protein (nectin) from S. faecalis membranes, which is required for the attachment of ATPase to the membrane. It is a heat-labile protein of low molecular weight and it is believed that the combination of ATPase, nectin, and an ATPase receptor site on the membrane may represent the mechanism for membrane biosynthesis. 

In Korn s view (1966), membrane protein rather than membrane lipid is the important functional group, contrary to the implications in the paucimolecular models. Korn visualized the first step in membrane biosynthesis as the synthesis of protein, and, according to the primary structure of the protein, lipid would be bound sequentially, forming lipoprotein. The globular subunits seen in electron micrographs could then be lipoprotein molecules. 

Kirschbaum, B. B., and Bosmann, H. B., 1973, Renal membrane biosynthesis and degradation. II. Localization and characterization of neuraminidase activity in rat kidney. Nephron 11 26-39. 

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