Regulation of guanylate cyclase in guinea-pig islets of Langerhans.
1. Guanylate cyclase activity was determined in homogenates of guinea-pig islets of Langerhans by measurement of the conversion of [alpha-(32)P]GTP into cyclic [(32)P]GMP, the reaction products being separated on columns of neutral alumina. 2. The pH optimum of the enzyme was 7.3; it showed a requirement for bivalent cations, the effectiveness of the cations tested being Mn(2+)>>Ca(2+)>Mg(2+). 3. About 70% of enzyme activity was sedimented by centrifugation at 105000g for 60min; activity was increased 2.3-fold by treatment of homogenates with 0.1% Triton X-100. 4. Guanylate cyclase activity of homogenates was increased by acetylcholine, secretin or pancreozymin, but was inhibited by adrenaline, noradrenaline or ATP. Insulin, glucagon, prostaglandins E(1) or E(2), glucose, F(-), diazoxide or glibenclamide were ineffective. 5. Determination of cyclic GMP amounts in islets by radioimmunoassay showed a basal concentration of 2.0pmol/mg of protein, which was increased by incubation of the islets in the presence of acetylcholine or the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine, but was unaffected by glucose. 6. Dibutyryl cyclic GMP had significant stimulatory effects on rates of insulin biosynthesis in isolated rat islets of Langerhans. 7. These results suggest a possible role for cyclic GMP in the regulation of insulin biosynthesis and secretion.
D000109:Acetylcholine / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002499:Centrifugation, Density Gradient; D002766:Cholecystokinin / Q000378:metabolism; D006152:Cyclic GMP / Q000378:metabolism; D004837:Epinephrine / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism; D006162:Guanylate Cyclase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D006168:Guinea Pigs; D006863:Hydrogen-Ion Concentration; D007328:Insulin / Q000096:biosynthesis; D007515:Islets of Langerhans / Q000201:enzymology*; D008274:Magnesium / Q000378:metabolism; D008297:Male; D008345:Manganese / Q000378:metabolism; D009638:Norepinephrine / Q000378:metabolism; D010761:Phosphorus Radioisotopes; D011092:Polyethylene Glycols; D011863:Radioimmunoassay; D051381:Rats; D012633:Secretin / Q000378:metabolism
D007328:Insulin; D010761:Phosphorus Radioisotopes; D012633:Secretin; D011092:Polyethylene Glycols; D008345:Manganese; D006160:Guanosine Triphosphate; D000255:Adenosine Triphosphate; D002766:Cholecystokinin; D006162:Guanylate Cyclase; D006152:Cyclic GMP; D008274:Magnesium; D000109:Acetylcholine; D002118:Calcium; D009638:Norepinephrine; D004837:Epinephrine