Properties and distribution of mammalian skeletal muscle guanylate cyclase. Alterations in denervated and dystrophic muscle

The distribution and kinetic properties of guanylate cyclase in normal, denervated and dystrophic muscle from lower hind limb muscle of rat and mouse were studied. Approximately 75% of the enzyme activity was in a high speed supernatant fraction (100.000 x g) and 15 to 20% in a particulate fraction (1,000 x g pellet). The particulate guanylate cyclase was found highly enriched in sarcolemma, increasing over 100-fold in specific activity. Following denervation the sarcolemmal and supernatant enzymes increased concomitantly and were 2-fold higher by 10 days. The Vmax of sarcolemmal guanylate cyclase increased from 1600 to 2800 pmol.5 min^-1.mg of protein^-1 over this period. The S_0.5 (0.13 mM), Hill coefficient (n= 1.7), Mn²⁺ dependency, inhibition by Ca²⁺, and degree of stimulation by Triton X-100 remained unchanged. Likewise, the Vmax of the 100,000 x g supernatant enzyme increased from 80 to 200 pmol.5 min^-1. mg^-1 with no change in the apparent Km (0.043 mM), Hill coefficient (n= 0.95), Mn²⁺ dependency, and degree of stimulation by Ca²⁺. The specific activity of particulate and supernatant enzymes was 2-fold higher in slow muscle (soleus) than in fast (extensor digitorum longus). Denervation increased the specific activity by approximately 2-fold in all cases. In mouse dystrophic muscle (129 ReJ dy/dy), the specific activity of the supernatant enzyme was 2.5-fold greater than that of control litter mates, while the particulate enzyme showed little change. Thus, the activities of particulate and soluble guanylate cyclase can change in a parallel fashion, as in denervation and in slow compared to fast muscle, and also can vary independently, as in dystrophic compared to normal muscle.