Phosphatidylinositol-specific phospholipase C activity of chromaffin granule-binding proteins.
Using [U-14C]phosphatidylinositol as substrate, Ca2+-dependent phospholipase C activity was detected in a group of bovine adrenal medullary proteins that bind to chromaffin granule membranes in the presence of Ca2+ ("chromobindins," Creutz, C. E., Dowling, L. G., Sando, J. J., Villar-Palasi, C., Whipple, J. H., and Zaks, W. J. (1983) J. Biol. Chem. 258, 14664-14674). The activity was maximal at neutral pH and represented an 80- to 240-fold enrichment of adrenal medullary cytosol phospholipase C activity measured at pH 7.3. The stimulation of activity by Ca2+ was complex; no activity was present in the absence of Ca2+, 25% activation occurred at 1 microM Ca2+, and full activation at 5 mM Ca2+. The enzyme bound to chromaffin granule membranes in the presence of 2 mM Ca2+ but was released at 40 microM Ca2+, suggesting that intrinsic enzyme activity may be regulated by [Ca2+] at 1 microM, but additional activation at higher concentrations of Ca2+ is seen in vitro as a result of Ca2+-dependent binding of the active enzyme to substrate-containing membranes. This enzyme may generate diacylglycerol and phosphorylated inositol to act as intracellular messengers in the vicinity of the chromaffin granule membrane during the process of exocytosis.
Creutz
C E
CE
Dowling
L G
LG
Kyger
E M
EM
Franson
R C
RC
D000313:Adrenal Medulla / Q000201:enzymology; D000818:Animals; D017310:Annexin A7; D017302:Annexins; D002118:Calcium / Q000494:pharmacology; D002135:Calcium-Binding Proteins / Q000378:metabolism*; D002250:Carbon Radioisotopes; D002417:Cattle; D002837:Chromaffin Granules / Q000201:enzymology*; D002838:Chromaffin System / Q000201:enzymology*; D003600:Cytosol / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007425:Intracellular Membranes / Q000201:enzymology; D007700:Kinetics; D008565:Membrane Proteins / Q000378:metabolism*; D010716:Phosphatidylinositols / Q000378:metabolism*; D010740:Phospholipases / Q000378:metabolism*; D011506:Proteins / Q000378:metabolism*; D013049:Spectrin; D010738:Type C Phospholipases / Q000378:metabolism*
D017310:Annexin A7; D017302:Annexins; D002135:Calcium-Binding Proteins; D002250:Carbon Radioisotopes; D008565:Membrane Proteins; D010716:Phosphatidylinositols; D011506:Proteins; C041393:spectrin-like proteins; D013049:Spectrin; D010740:Phospholipases; D010738:Type C Phospholipases; D002118:Calcium