Glycoproteins mitochondrial

The illustration shows a model of a small section of a membrane. The phospholipids are the most important group of membrane lipids. They include phosphatidylcholine (lecithin), phosphatidylethanolamine, phos-phatidylserine, phosphatidylinositol, and sphingomyelin (for their structures, see p. 50). in addition, membranes in animal cells also contain cholesterol (with the exception of inner mitochondrial membranes). Clycoli-pids (a ganglioside is shown here) are mainly found on the outside of the plasma membrane. Together with the glycoproteins, they form the exterior coating of the cell (the gly-cocalyx). 

Biological membranes consist primarily of proteins and lip-ids. The relative amounts of these materials vary considerably, depending on the source of the membrane. At one extreme, the inner mitochondrial membrane is about 80% protein and 20% lipid by weight at the other, the myelin sheath membrane is about 80% lipid and 20% protein. The plasma membrane of human erythrocytes contains about equal amounts of protein and lipid. Many membranes also contain small amounts of carbohydrates. These almost always are covalently attached to either proteins (as glycoproteins) or lipids (as glycolipids or lipopolysaccharides). The mitochondrial inner membrane has little or no carbohydrate, but the myelin membrane has about 3% carbohydrate by weight, and the erythrocyte plasma membrane about 8%. 

The proteins that are responsible for mitochondrial Ca2+ uptake have not been identified with certainty. Various glycoproteins isolated from mitochondria are probably Ca2+ receptor proteins rather than Ca24 transporters. However, a 3000 molecular weight Ca2+-binding protein has been isolated from the inner membrane of calf heart mitochondria which has properties appropriate... 

Enzymes are found at different locations within cells. AST, ALT, and LD are cytosolic enzymes. As such, they can be released with cell injury, and appear in plasma relatively rapidly. In the case of AST and ALT, there are both mitochondrial and cytosolic isoenzymes in hepatocytes and other cells containing these enzymes. In the case of ALT, the relative amount of mitochondrial isoenzyme is small, and its plasma half-life is extremely short, making it of no diagnostic significance. In the case of AST, the mitochondrial isoenzyme represents a significant fraction of total AST within hepatocytes. In contrast, ALP and GGT are membrane-bound glycoprotein enzymes. The most important location of both enzymes is on the canalicular membrane of hepatocytes. 

Cholesterol biosynthesis proceeds via the isoprenoids in a multistep pathway. The end product, cholesterol, and the intermediates of the pathway participate in diverse cellular functions. The isoprenoid units give rise to dolichol, CoQ, heme A, isopentenyl-tRNA, famesylated proteins, and vitamin D (in the presence of sunlight and 7-dehydrocholesterol). Dolichol is used in the synthesis of glycoproteins, CoQ in the mitochondrial electron transport chain, famesylation and geranylgeranylation by posttrans-lational lipid modification that is required for membrane association and function of proteins such as p2V and G-protein subunits. 

Ox liver mitochondria were swollen in hypotonic Tris buffer and then were shrunk in hypertonic sucrose. This technique liberated a mitochondrial glycoprotein which was purified by preparative electrophoresis... 

Cellular metabolites derived from mevalonic acid are required for cell proliferation. Cholesterol Is an essential component of cell membranes, farnesyl pyrophosphate is required to covalently bind to intracellular proteins and modify their function, ubiquinone is required for mitochondrial electron transport, and dolichol phosphates are required for glycoprotein synthesis. 

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