Measurement of cGMP and soluble guanylyl cyclase activity.

Soluble guanylyl cyclase is responsible for synthesis of guanosine 3'5'-cyclic monophosphate. The enzyme is activated by NO, so measurement of tissue levels of cGMP and the activity of guanylyl cyclase is important in studies of NO-cGMP signal transduction. The method of choice for measuring tissue levels of cGMP is a radioimmunoassay, but it can also be measured using a scintillation proximity assay. Guanylyl cyclase activity is determined by measuring the conversion of GTP to cGMP using a radioimmunoassay or by following the conversion of [³²P]GTP to [³²P]cGMP, with separation of the product by precipitation and chromatography on an alumina column.