Receptor enzyme coupled

There are several ways in which CLA may cause an increase in CPT activity. First, CLA can modify the fatty acid composition of the cell membrane, thus altering the receptor-enzyme coupling that may enhance fatty acid oxidation by stimulating CPT activity. Second, CLA may activate peroxisome proliferator-activated receptors (PPAR), which in turn may enhance fatty acid oxidation (21-23). 

Rajerison, R., Marchetti, J., Roy, C., Bockaert, J., and Jard, S., 1974, The vasopressin-sensitive adenylate cyclase of the rat kidney Effect of adrenalectomy and corticosteroids on hormonal receptor-enzyme coupling, J. Biol. Chem. 249 6390. 

Enzyme coupled receptors Signal activates an enzyme activity of the receptor itself—tyrosine kinases, phospholipase C. 

For enzyme coupled receptors, activation of the receptor turns the receptor itself into an active enzyme. This activity may belong to the receptor itself, but sometimes activation of the receptor recruits and activates a separate enzyme through adaptor molecules (Fig. 9-3). A common mechanism of activation of these receptors involves dimerization. The signal molecule causes individual molecules of the receptor to associate with themselves in the membrane. Once dimerized, the receptors become activated and gain enzyme activity. 

Recently, it was shown that the thromboxane receptor itself is a substrate ofcGMP-PK and cAMP-PK in HEK293 cells, HEL cells, or with purified enzymes in vitro. Phosphorylation of its cytoplasmic carboxyterminal domain prevented the thromboxane receptor from coupling to and activating G-proteins [36, 37]. For intact platelets, TxA2 receptor phosphorylation has not yet been shown, however, it would provide another explanation for the inhibition of PLC activation and subsequent intracellular Ca2+ elevation and granule secretion in response to cyclic nucleotides. 

Alpf receptors are coupled via G proteins in the Gq family to phospholipase C. This enzyme hydrolyzes polyphosphoinositides, leading to the formation of inositol 1,4,5-trisphosphate (IP3) and diacylglycerol (DAG) (Table 9-1, Figure 9-1). IP3 promotes the release... 

A second class of serpentine receptors are coupled through a G protein to a plasma membrane phospholipase C (PLC) that is specific for the plasma membrane lipid phosphatidylinositol 4,5-bisphosphate (see Fig. 10-15). This hormone-sensitive enzyme catalyzes the formation of two potent second messengers diacyl-glycerol and inositol 1,4,5-trisphosphate, or IP i (not to be confused with PIP3, p. 431). 

Another similar class of receptors are coupled to G, proteins. When activated, these G proteins in turn activate a variety of effectors as indicated in table 24.5. One of these effectors is adenylate cyclase again, but in this case the ar GTP subunit inhibits enzyme activity, thus lowering cAMP levels. The list of known G proteins is increasing at a rapid pace. 

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