Phospholipase C activity in membranes and a soluble fraction isolated from frog skeletal muscle.
Highly purified triads and transverse tubules, as well as soluble fraction isolated from frog skeletal muscle, hydrolyze exogenous phosphatidylinositol 4,5-bisphosphate forming inositol 1,4,5-trisphosphate with maximal rates in the range 0.5-1 nmol/mg per min at pCa 3. Sarcoplasmic reticulum membranes present a minor activity. The hydrolysis rates in triads were 0.072 +/- 0.015 nmol/mg per min at pCa 7, increasing to 0.263 +/- 0.026 nmol/mg per min at pCa 5 with 1.0 mM Mg and 0.1 mM substrate. The phospholipase C activity of isolated transverse tubules at pCa 3 was 0.570 +/- 0.032 nmol/mg per min. Since triads contain 10% transverse tubules, and correcting for the small contribution of sarcoplasmic reticulum, the calculated phospholipase C activity of transverse tubules at pCa 3 is about 10-times higher than the observed values, suggesting loss of activity during isolation. The activation by calcium was also observed in a soluble fraction and was neither replaced nor inhibited by magnesium. No effect of GTP analogs on phospholipase C activity was detected.
Departamento de Fisiología y Biofísica, Facultad de Medicina, Universidad de Chile, Santiago.
M
M
Angélica Carrasco
J
J
Sierralta
C
C
Hidalgo
D000818:Animals; D002118:Calcium / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000378:metabolism; D008274:Magnesium / Q000494:pharmacology; D008566:Membranes / Q000201:enzymology; D009132:Muscles / Q000201:enzymology* / Q000648:ultrastructure; D019269:Phosphatidylinositol 4,5-Diphosphate; D018129:Phosphatidylinositol Phosphates / Q000378:metabolism; D011898:Ranidae; D012519:Sarcoplasmic Reticulum / Q000201:enzymology; D014316:Tritium; D010738:Type C Phospholipases / Q000378:metabolism*
D019269:Phosphatidylinositol 4,5-Diphosphate; D018129:Phosphatidylinositol Phosphates; D014316:Tritium; D010738:Type C Phospholipases; D019204:GTP-Binding Proteins; D008274:Magnesium; D002118:Calcium