Properties of membrane-bound and soluble guanylate cyclase of cardiac and skeletal muscle.

Kinetic properties of guanylate cyclase present in the washed particles, plasma membranes, and the soluble cytoplasm of heart and skeletal muscle are described; properties of the enzyme solubilized by Triton X-100 treatment of the particles or membrane fractions are also reported. It is apparent from the data that the membrane-bound guanylate cyclase in the cell may be regulated by acetylcholine, may exist as a metallo-protein with bound Mn2+ (essential for activity), and that Mg2+ regulates, whereas Ca2+ and nucleotides (especially ATP) modulate, guanylate cyclase activity. The findings also suggest that guanylate cyclase, similar to adenylate cyclase and (Na+, K+)-ATPase, is mainly located in the plasma membranes of heart and skeletal muscle.