Lipid and membrane metabolism

Lipid and Membrane Metabolism of the Malaria Parasite and the African Trypanosome... 

Comparison of the lipids and lipid and membrane metabolism of the malaria parasite and the African typanosome with that of their environments emphasizes the unique ways in which parasites are able to access the nutrients available, and modify them to their advantage. 

Fatty acyl-CoA desaturases are terminal oxidases of a membrane-bound enzyme complex that also includes cytochrome b5 and cytochrome b5 reductase (Bloomfield and Bloch, 1960). They remove substrate hydrogen atoms at a position determined by the specificity of the enzyme. They play essential roles in regulating membrane fluidity and are also involved in insect lipid and pheromone metabolism. They share the presence of three highly conserved histidine-rich sequences (H-boxes) that coordinate the diiron-oxo structure at the active sites (Shanklin and Cahoon, 1998) and four hydrophobic a helices that appear to anchor the protein into the lipid bilayer and situate the H-boxes in their correct position in the active site. 

The chemistry of phosphate esters and anhydrides is so central to biochemistry that the subject might also be logically discussed in the sections on nucleic acids, lipids and membranes, or intermediary metabolism. However, because of the importance of sugar phosphates and their derivatives in Experiment 12, the subject is presented in this section. The background is important to more than Exper-... 

Cr(III) is held to be essential for human and animal nutrition, necessary for the maintenance of glucose, lipid, and protein metabolism, and is therefore used as a dietary supplement mostly in the form of its picolinate or nicotinate. Trivalent chromium is poorly absorbed principally because, unless heavily com-plexed, it will precipitate under most physiological pH conditions. Whilst Cr(III) compounds appear to be able to produce genetic effects with purified nucleic acids or cell nuclei, there is generally no such activity in intact cellular systems due to the relatively poor ability of Cr(III) to cross cell membranes. 

Membrane preparations from lactating bovine mammary glands have been shown to incorporate o-mannose from GDP-o-mannose into lipid and into metabolically stable acceptors." It is postulated that the sequence GDP-o-mannose P -D-mannosyl-P -pyrophosphorylisoprenol P -o-mannosyl-oligosaccharide-P -pyrophosphoryl o-mannoprotein is followed. The structure of the oligosaccharide-lipid and the endogenous glycoproteins were not established. 

Other probable effects of co-3 fatty acids are membrane-mediated prcxosses, such as insulin transduction signals activity of lipases, which are affected by alteration of the fatty acid composition of the membrane phospholipids and regulation of genes involved in lipid and glucxrse metabolism, and adipogenesis. ... 

Thompson, G.A., 1996. Lipids and membrane function in green algae. Biochimica et Biophysica Acta (BBA)-lipids and Lipid Metabolism 1302 (1), 17-45. 

Brindley, D.N. (1985) Metabolism of triacylglycerols, in Biochemistry of Lipids and Membranes (eds D.E. Vance and J.E. Vance), Benjamin/Cummings, Menlo Park, CA, USA. 

Merrill AH, Sweeley CC Sphingolipids metabolism and cell signaling. In Biochemistry of Lipids, Lipoproteins and Membranes. Vance DE, Vance JE (editors). Elsevier, 1996. 

Like other cells, a neuron has a nucleus with genetic DNA, although nerve cells cannot divide (replicate) after maturity, and a prominent nucleolus for ribosome synthesis. There are also mitochondria for energy supply as well as a smooth and a rough endoplasmic reticulum for lipid and protein synthesis, and a Golgi apparatus. These are all in a fluid cytosol (cytoplasm), containing enzymes for cell metabolism and NT synthesis and which is surrounded by a phospholipid plasma membrane, impermeable to ions and water-soluble substances. In order to cross the membrane, substances either have to be very lipid soluble or transported by special carrier proteins. It is also the site for NT receptors and the various ion channels important in the control of neuronal excitability. 

The reported (14) mechanisms of action of allelochemlcals Include effects on root ultrastructure and subsequent Inhibition of Ion absorption and water uptake, effects on hormone-induced growth, alteration of membrane permeability, changes In lipid and organic acid metabolism, inhibition of protein synthesis and alteration of enzyme activity, and effects on stomatal opening and on photosynthesis. Reduced leaf water potential Is one result of treatment with ferulic and p-coumaric acids (15). Colton and Einhellig (16) found that aqueous extracts of velvetleaf (Abutllon theophrastl Medic.) Increased diffusive resistance In soybean fGlycine max. (L.) Merr.] leaves, probably as a result of stomatal closure. In addition, there was evidence of water stress and reduced quantities of chlorophyll In Inhibited plants. 

LBPs are likely to have conventional roles in the energy metabolism and transport of lipids in nematodes for membrane construction, etc. Many parasitic helminths have deficiencies in the synthesis of some lipids and so their lipid acquisition, transport and storage mechanisms clearly need to be specialized and therefore pertinent to the host-parasite relationship (Barrett, 1981). From a practical point of view, lipid transporter proteins may also be important in the delivery of anthelmintic drugs to their target most anthelmintics are hydrophobic and if they do not distribute to their site of action within the parasites by simple diffusion across and along membranes, then the parasite s own carrier proteins may be involved. 

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