Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:4.6.1.1 (adenylate cyclase)
 19,190 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The ligand-induced internalization of the hepatic glucagon receptor has been studied in rats in vivo using cell fractionation. Injection of glucagon (11 nmol/100 g BW) led to a 2- to 3-fold increase in glucagon-binding activity in Golgi-endosomal (GE) fractions along with a 10-20% decrease in binding activity in plasma membrane (PM) fractions. These changes were time and dose dependent, reaching a maximum by 12-24 min and undergoing reversal in 2 h. Glucagon injection also caused a 20% decrease in glucagon binding to the total particulate fraction, which did not occur when binding was measured in the presence of the detergent octylglucoside. The change in glucagon-binding activity in PM and GE fractions resulted mainly from a change in receptor number; affinity remained unaffected (apparent Kd, 0.5 and 5 nM, respectively). A 5- to 10-fold increase in the glucagon content of GE fractions was observed in glucagon-treated rats. Neither the distribution of PM and Golgi marker enzymes nor that of the asialoglycoprotein receptor was affected by glucagon treatment. Regardless of glucagon treatment, glucagon receptors in GE fractions were less sensitive to GTP than receptors in PM fractions with respect to both inhibition of steady state binding and dissociation of prebound ligand. On sodium dodecyl sulfate-polyacrylamide gel electrophoresis, glucagon-receptor complexes formed in PM and GE fractions and subsequently cross-linked showed the same apparent mol wt (57 kilodaltons). In addition, they were identically sensitive to N-glycanase treatment, with two major species of lower mol wt generated. However, only cross-linked complexes associated with PM fractions showed detectable GTP sensitivity. GE fractions displayed a GTP-sensitive adenylate cyclase activity that was about 12 times lower than that of PM fractions. In both fractions, activity was stimulated by the addition of forskolin (8-fold) and, to a lesser extent, glucagon (3-fold). In vivo glucagon treatment led to an increase in activity in GE, but not PM, fractions. These results are consistent with the view that upon acute occupancy, hepatic glucagon receptors are rapidly and specifically internalized along with their ligand. During this process, receptor retained structural integrity and uncouple, albeit partially, from other components of the adenylate cyclase system.
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PMID:Ligand-mediated internalization of glucagon receptors in intact rat liver. 131 25

Point mutations in the luteinizing hormone/human chorionic gonadotropin (LH/hCG) receptor have been shown to cause constitutive activation which results in precocious puberty in affected males. We introduced one of these mutations, Asp-556 --> Gly, into the rat LH/hCG receptor and demonstrated that the mutant receptor constitutively activated adenylate cyclase in transfected 293 T cells. The cell surface expression of the mutant receptor was lower than that of the wild type receptor. Pulse-chase studies showed that the 73-kDa precursor of both the mutant and wild type receptors was synthesized at comparable efficiencies. However, post-translational processing of the mutant receptor to the mature 92-kDa form, which has N-linked complex type oligosaccharide chains, was impaired. Sensitivity of the mutant receptor to peptide-N-glycanase F and endoglycosidase H, and insensitivity to sialidase indicated that the 73-kDa species represents the high mannose form that has not yet been trafficked through the medial and trans Golgi. Additionally, although the wild type receptor was palmitoylated, the mutant receptor was not. Although the high mannose 73-kDa species is capable of binding LH/hCG, our results show that post-translational processing in the Golgi is required for the mature 92-kDa receptor to reach the cell surface.
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PMID:Post-translational processing in the Golgi plays a critical role in the trafficking of the luteinizing hormone/human chorionic gonadotropin receptor to the cell surface. 903 11

Prolonged treatment of human platelets with the adenylate cyclase-stimulating prostacyclin analog iloprost leads to reduction in cAMP formation. Previous studies have demonstrated that this may be ascribed to modification of both receptor and Gsalpha function rather than of the catalytic component of adenylate cyclase [Mollner, S., Deppisch, H. & Pfeuffer, T. (1992) Eur. J. Biochem. 210, 539-544]. Iloprost-induced desensitization was accompanied by the formation of a Gsalpha-containing 90-kDa product in membranes treated with the bifunctional cross-linker 1,6-bismaleimidohexane. The cAMP-inducing prostanoid PGD2, which does not promote desensitization, did not cause formation of the 90-kDa species either. The long-term effect of the common G-protein activator [AlF4]- on human platelet adenylate cyclase was shown in many respects to be comparable with that of iloprost. However, [AlF4]- treatment also failed to induce the 90-kDa species, showing that different mechanisms of desensitization were operating. Treatment of the cross-linked 90-kDa complex with PNGase F demonstrated the glycoprotein nature of the Gsalpha-associated component. The 90-kDa cross-linked product was purified by consecutive immunoaffinity chromatography and preparative PAGE to apparent homogeneity. Analysis of the purified protein by MS suggested that, besides Gsalpha, the heavy chain of MHC I (HLA-A2) was part of the complex. This was confirmed by coprecipitation of Gsalpha by the monoclonal anti-(MHC I) antibody W6/32.
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PMID:Selective formation of Gsalpha-MHC I complexes after desensitization of human platelets with iloprost. 991 89