Membrane-bound and soluble guanylyl cyclases

Guanylyl cyclase catalyses the reaction GTP — cGMP + pyrophosphate (PP ). Heart stress (e.g. atrial stretch due to increased blood pressure and hence increased cardiac muscle work) 

A further type of PM-located GC is gastrointestinal (GI) C-type GC that is activated by the paracrine peptide hormone guanylin. Guanylin is secreted by GI cells and resultant GC activation and cGMP elevation results in increased Cl transport via the cystic fibrosis transmembrane conductance regulator (CFTR) into the intestinal lumen with resultant increased water flow. The Escherkhia coli heat-stable enterotoxin mimics guanylin in activating this intestinal C-type GC and consequently causes diarrhoea. 

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