Alpha subunit of soluble guanylate cyclase (sGC), a central enzyme in nitric oxide (NO) signaling. Functions as the main intracellular receptor for NO. Upon NO binding, catalyzes the conversion of GTP to cyclic GMP (cGMP) and thereby transducing NO signal into a ubiquitous intracellular second messenger. . [Isoform 2]: Acts as a negative regulator of guanylyl cyclase activity as it forms non-functional heterodimers with the beta subunit. . This is the function of ENSG00000152402 (GUCY1A2, guanylate cyclase 1 soluble subunit alpha 2).