Murad’s enzyme activation

Ferid Murad knew that nitroglycerine caused relaxation of smooth muscle cells. The enzyme, guanylyl cyclase, was activated and increased cyclic GMP, causing relaxation of the muscle. Did nitroglycerin act via release of nitric oxide, NO? He bubbled NO-gas through tissue containing the enzyme; cyclic GMP increased! A new mode of drug action had been discovered!
NO induces synthesis of cGMP by stimulation of GC leading to relaxation of myosin (muscle protein)
 Acetylcholine stimulates the endothelial cells to produce a factor, NO, which penetrates into and activates the muscle cells causing relaxation.

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