Enzyme kinase

Basically, AZT is anabohcaHy phosphorylated to AZT mono-, di-, and tri-phosphates by various enzymes (kinases) of a target ceU (159). AZT-triphosphate competes with other phosphorylated pyrimidine nucleosides for incorporation into HIV DNA by the viral reverse transcriptase. Incorporation of the AZT-triphosphate into reverse transcriptase results in viral DNA chain termination. Reverse transcriptase is essential in the repHcative cycle of HIV. 

Calcium receptors Membranes of vesicles. Many enzymes (kinases). 

Proportional to this oxidation energy can and must be stored by phosphorylation of carboxylate and sugar substrates which is done by Mg or Zn enzymes (kinases, phosphatases) mainly. 

In muscle and adipose tissue, insulin promotes transport of glucose and other monosaccharides across cell membranes it al.so facilitates tran.sport of amino icids, potassium ion.s. nucleosides, and ionic phosphate. Insulin also activates certain enzymes—kinases and glycogen. synthetase in muscle und adipose tissue. In adipose tissue, insulin decreases the release of fatty acids induced by epinephrine or glucagon. cAMP promotes fatty acid release from adipose ti.ssue therefore. it is pos.sible that insulin decreases fatty acid release by reducing tissue levels of cAMP. Insulin also facilitates the incorporation of intracellular amino acids into protein. 

When the activator ion is an essential part of the functional enzyme molecule, whether as a purely structural element or with an additional catalytic role, it is usually incorporated quite firmly into the enzyme molecule. Therefore it is not usually necessary to add the activator to reaction mixtures, and excess of the ion may even have an inhibitory effect. However, in some cases the activating ion is attached only weakly or transiently to the enzyme (or its substrate) during catalysis. Enzyme samples may therefore be deficient in the ion so that addition of the ion increases the reaction rate or indeed may be essential for the reaction to take place. For example, all phosphate transfer enzymes (kinases), such as creatine kinase, require the essential pres-... 

Oluconate Metabolism. Gluconate is oxidized to 2-ketogluconate by incompletely described bacterial enzymes. Kinases have been found for phosphorylating both gluconate and its 2-keto derivative. 2,5-Diketo-gluconate has been described as a product in some systems. Eventually this pathway leads to the Krebs cycle, but it is not known how. 

Divalent cations, univalent cations, or both are essential cofactors for a large number of enzymes. Kinases as a class, for example, share the requirement for such cations, while in other instances, other metal ions are inhibitors of metal-activated enzymes, e.g., activation by Mg " and inhibition by Ca for many kinases and synthetases. Mildvan (1970) has reviewed the models that have been proposed to account for activation (or inhibition) of enzymes by metal ions. The "substrate bridge" and "metal bridge" models conceive of the metal ions either combining with the substrate to form a chelate or interacting with the enzyme to complete the required binding site. These complexes usually involve the active site, but Schramm (1974) has demonstrated activation of AMP nucleosidase by MgATP at a modifier site instead. 

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