Guanyl cyclases, transmembrane

The ANP leceptoi exists in two forms, ANP and ANPg, both of which have been cloned. These membrane-bound guanylate cyclases have a single transmembrane domain, an intracellular protein kinase-like domain, and a catalytic cyclase domain, activation of which results in the accumulation of cychc guanosine monophosphate (cGMP). A third receptor subtype (ANP ) has been identified that does not have intrinsic guanylate cyclase activity and may play a role in the clearance of ANP. 

Receptor Single transmembrane a helix intrinsic guanylate cyclase activity in... 

There are two major families of guanylate cyclase, the particulate-associated enzymes, which are actually transmembrane receptors that contain guanylate cyclase within their intracellular domains, and the soluble type activated by NO (Kimura and Murad, 1974 Kuno et al., 1986 Schulz et al., 1991 Garbers, 1992 Schmidt et al., 1993). With more details of the structure and function of these enzymes, however, this strict division may become blurred. For example, NO-stimulated guanylate cyclase activity has been found to be associated with the membrane fraction of cells in some cases (Murad, 1994). 

The mechanism of activation of the receptor-type guanylate cyclases is not entirely clear. As is the case with other single-transmembrane domain receptor types, such as receptor-type tyrosine kinases, some sort of dimerization may be induced by ligand binding, which serves to activate the intracellular enzyme part of the receptor. As discussed in the next section, dimerization is essential to enzyme activity in soluble guanylate cyclases. 

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