Effect of L-alpha-phosphatidylinositol on a vascular smooth muscle Ca2+-dependent protease. Reduction of the Ca2+ requirement for autolysis.

Abstract

Vascular smooth muscle contains large amounts of a Ca2+-dependent protease. Similar to a Ca2+-dependent protease previously purified from chicken gizzard smooth muscle (Hathaway, D. R., Werth, D. K., and Haeberle, J. R. (1982) J. Biol. Chem. 257, 9072-9077), the mammalian vascular muscle protease is a heterodimer consisting of 76,000- and 30,000-dalton subunits (IIa). The enzyme can undergo autolysis in the presence of Ca2+ to produce a smaller species consisting of 76,000- and 18,000-dalton subunits (IIb). Autolysis greatly reduces the Ca2+ dependence of catalytic activity. The autolytic species, IIb, was approximately 23-fold more sensitive to Ca2+ (K0.5 = 39 microM) than the native enzyme, IIa (K0.5 = 891 microM). In this communication, we report that phosphatidylinositol and to a lesser extent one metabolic derivative, dioleoylglycerol, stimulate autolysis of the vascular Ca2+-dependent protease by reducing the Ca2+ for autolysis from K0.5 = 680 microM in the absence of lipid to K0.5 = 87 microM in the presence of both phosphatidylinositol and dioleoylglycerol. Moreover, the reduction in the Ca2+ requirement for autolysis produced by the phosphatidylinositol was antagonized by the phospholipid-binding drug, trifluoperazine. In addition, the effect of phosphatidylinositol was specific for autolysis, and none of several phospholipids or derivatives tested altered the Ca2+ dependence or maximal rate for protein degradation of the autolytic product, IIb. Our results suggest that autolysis may be an important initial step in the activation of the Ca2+-dependent protease in vascular smooth muscle and that this step may be regulated by a combination of Ca2+ and phosphatidylinositol.

• Authors: S A Coolican, D R Hathaway
• Journal: The Journal of biological chemistry (J Biol Chem) Vol. 259 Issue 19 Pg. 11627-30 (Oct 10 1984) ISSN: 0021-9258 [Print] United States
• PMID: 6090440 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't, Research Support, U.S. Gov't, P.H.S.)

Chemical References

• Diglycerides
• Phosphatidylinositols
• Endopeptidases
• Calpain
• Calcium
• diolein

Topics

• Animals
• Calcium (metabolism)
• Calpain
• Cattle
• Diglycerides (pharmacology)
• Electrophoresis, Polyacrylamide Gel
• Endopeptidases (metabolism)
• Kinetics
• Molecular Weight
• Muscle, Smooth, Vascular (enzymology)
• Phosphatidylinositols (pharmacology)