Guanosine 5-thio diphosphate

Authi KS, Rao GHR, Evenden BJ, Crawford N (1988) Action of Guanosine 5 -(beta-thio)Diphosphate on Thrombin-Induced Activation and Calcium Mobilization in Saponin-Permeabilized and Intact Human Platelets. Biochem J 255 885... 

Inhibition of forskolln stimulated adenylate cyclase in membranes by guanine nucleotides can be observed when a functional Ni subunit Is present and has been shown in membranes from rat brain,34 s49 lymphoma cells, 28,66 rat adipocytes, and human platelets. This inhibition can be observed with GTP, GppNHp, or GTP-yS (guanosine 5 -(3-0-thlo)triphosphate), is blocked by GDP or GDP-gS (guanosine 5 (2-0-thio)diphosphate), and does not require the presence of an inhibitory hormone. Guanine nucleotide Inhibition of adenylate cyclase is not competitive with forskolln and is not observed when membranes are... 

The involvement of a gnanosine triphosphate (GTP)-hindmg protein coupling occupancy of receptors by somatostatin and acetylcholine (or car-bachol) to activation of channels was demonstrated by three types of experiments (Yatani et al. 1987) 1) channels activated in the cell-attached mode did not remain active if, after excision, they were placed into solutions without GTP or if in the presence of GTP, excess of the inhibitor guanosine [P-thio]diphosphate was added 2) addition of guanosine [P-thio] diphosphate (100 pM) to patches excised without prior activation by ligands led, after lag times that varied between 2 to 10 min, to activation of IG channels with the same unit con-... 

The subsequent cleavage of the thio-ester succinylCoA into succinate and coenzyme A by succinic acid-CoA ligase (succinyl CoA synthetase, succinic thiokinase) is strongly exergonic and is used to synthesize a phosphoric acid anhydride bond ( substrate level phosphorylation , see p. 124). However, it is not ATP that is produced here as is otherwise usually the case, but instead guanosine triphosphate (CTP). However, GTP can be converted into ATP by a nucleoside diphosphate kinase (not shown). 

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