Properties of particulate, membrane-associated and soluble guanylate cyclase from cardiac muscle, skeletal muscle, cerebral cortex and liver.
1. Guanylate cyclase of washed particles and plasma membranes showed S-shaped progress curves when titrated with either GTP or Mn2+ ions; similar results were obtained with Triton X-100-solubilized enzyme preparation from washed particles. Hill plots of these data revealed multiple metal-nucleotide and free-metal binding sites. 2. Guanylate cyclase of supernatant fractions displayed typical Michaelis-Menten properties when enzyme required excess of (free) Mn2+ (over GTP) for maximal activities; Ka (free Mn2+) was about 0.15-0.25 mM at subsaturating concentrations of GTP. 4 MnATP, MnADP, and MnGDP were found to increase the activities of both particulate and superantant enzyme, when MnGTP concentration was below saturation and free Mn2+ ion concentration was low (less than 100 muM); MnATP (50muM-1 mM) inhibited both these activities at high free Mn2+ concentration (1.5 mM) and inhibition of the particulate enzyme was greater than that of supernatant enzyme. 5. Ca2+ ions stimulated supernatant-enzyme activity; the stimulatory concentration of Ca2+ ions depended on the concentration of Mn2+ and GTP. 6. A modest stimulation of particulate guanylate cyclase by pyrophosphate (0.02-1 mM) was observed; the pyrophosphate effect appeared to be competitive with respect to GTP. At a higher concentration (2 mM), pyrophosphate produced a marked inhibition of particulate enzyme; the nature of inhibitory effect appeared complex. 7. Inorganic salts (e.g. NaCl, KCl, LiBr, NaF) produced inhibition of particulate enzyme; the degree of inhibition of Triton X-100-stimulated activity was less than that of unstimulated activity. 9. Treatment of sarcolemmal or microsomal membranes with either phospholipase C or trypsin decreased, whereas phospholipase A increased, the activity of guanylate cyclase.
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002462:Cell Membrane / Q000201:enzymology; D002540:Cerebral Cortex / Q000201:enzymology*; D011756:Diphosphates / Q000494:pharmacology; D006160:Guanosine Triphosphate / Q000378:metabolism; D006162:Guanylate Cyclase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D006168:Guinea Pigs; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D008345:Manganese; D009132:Muscles / Q000201:enzymology*; D009206:Myocardium / Q000201:enzymology*; D010740:Phospholipases / Q000494:pharmacology; D011817:Rabbits; D051381:Rats; D013347:Subcellular Fractions; D014357:Trypsin / Q000494:pharmacology
D011756:Diphosphates; D008345:Manganese; D006160:Guanosine Triphosphate; D000255:Adenosine Triphosphate; D010740:Phospholipases; D014357:Trypsin; D006162:Guanylate Cyclase; D002118:Calcium