Microsomal phosphate transport

Microsomal phosphate transport protein (T2Q ) which mediates the efflux of P , an inhibitor of the glucose-6-phosphatase, from the lumen of the endoplasmic reticulum to the cytosol ... 

Pederson, T.C., Buege, J.A. and Aust, S.D. (1973). Microsomal electron transport. The role of reduced nicotinamide dinucleotide phosphateliver microsomal lipid peroxidation. J. Biol. Chem. 248, 7134—7141. 

Leuzzi R, Banhegyi G, Kardon T, Marcolongo P, Capecchi PL, 42. Burger, HJ, Benedetti A, Fulceri R. Inhibition of microsomal glucose-6-phosphate transport in human neutrophils results in apoptosis a potential explanation for neutrophil dysfunction in 43. glycogen storage disease type lb. Blood 2003 101 2381-2387. 

Microsomal phosphate/pyrophosphate transport protein M.W. 37,000), which transports phosphate, pyrophosphate, and carbamoyl phosphate, which are substrates for glucose-6-phosphatase and... 

Glucose-6-phosphate transporter in hepatocyte microsomal membrane Phosphate transporter in hepatocyte microsomal membrane... 

Hrycay EG, O Brien PJ (1973) Microsomal electron transport. 1. Reduced nicotinamide adenine dinucleotide phosphate-cytochrome c reductase and cytochrome P-450 as electron carriers in microsomal NADPH-peroxidase activity. Arch Biochem Biophys 157 7-22... 

The active forms of the D vitamins are la,25-dihydroxy-vitamin Dj and 25-hydroxy-vitamin Dj. They are formed by enzymatic hydroxylation in the liver microsomes and then in the kidney mitochondria by a ferredoxin flavoprotein and cytochrome P-450. The 1,25-dihydroxy vitamin is then transported to the bone, intestine, and other target organs (kidneys, parathyroid gland). Consequently, it can be considered a hormone since it is produced in one organ but used elsewhere. It mobilizes calcium and phosphate and also influences the absorption of these ions in the intestine, thus promoting bone mineralization. The hormone is also active in relieving hypoparathyroidism and postmenopausal osteoporosis, which, for example, results in the brittle bones of elderly women. 

The concentration of calcium in extracellular fluids is 10 M, and the concentration of cytoplasmic calcium is 10 M. The mitochondria and microsomes contain 90 to 99% of the intracellular calcium, which is bound largely to organic and inorganic phosphates. The low cytoplasmic concentration of calcium is maintained by three calcium pump-leak-transport systems. Each pump is oriented in a direction of calcium egress from the cytosol (see also Figure 84). 

The enzymes responsible are found in the albatross salt gland (Hokin and Hokin, 1960), erythrocyte membranes (Holdn and Hokin, 1961), and brain microsomes (Hokin and Hokin, 1959b). Mcllwain (1963) has criticized the scheme on quantitative grounds, making the point among others that the observed rates for the enzymatic reactions involved in cerebral tissue are about 0.02% of tiie rates of cation transport. It is still not proved, in fact, whether the increased exchange of phosphate with phosphatidic acid in membranous systems in the presence of acetylcholine is a secondary result of an action of the drug on some other system. 

Glycogen storage disease type I is characterized by deficient activity of the glucose-6-phosphatase enzyme systan. The glucose-6-phosphatase enzyme is located in the endoplasmic reticulum (ER) (microsomal fraction). Glucose-6-phosphate must first be transported from the cytoplasm into... 

Proteins are hydrolyzed to amino acids, which enter the Krebs cycle after transportation in the blood and transamination in the liver. The reversal of the Krebs cycle and the Embden-Meyerhof pathway converts the Krebs cycle substrates into glucose. The conversion of glucose-6-phosphate to glucose is catalyzed by a microsomal enzyme, glucose-6-phosphatase. The mechanisms controlling gluconeogenesis are discussed in more detail in Chapter 16. 

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