Cardiolipin-sensitive phospholipase C in subcellular fractions of rabbit myocardium.
Phosphatidylinositol-specific phospholipase C was characterized in the soluble phase and in membrane fractions prepared from rabbit myocardium. Four subforms of soluble phospholipase C were identified and characterized. Activity of one subform was inhibited 80% when cardiolipin was present in substrate vesicles, whereas three subforms were stimulated 2- to 10-fold by cardiolipin. A cationic subform, molecular mass 67 kDa, was stimulated threefold when cardiolipin comprised 2% of the total phospholipid and fivefold when it comprised 12%. The major mechanism for the cardiolipin effect was a decrease in the apparent Michaelis constant (Km) of this subform for substrate. Competition experiments were consistent with binding of this subform to cardiolipin. Phospholipase C activity was present in mitochondrial, microsomal, and sarcolemmal membrane fractions that were essentially free of contamination by cytosol. Detection of membrane-associated phospholipase C was facilitated by cardiolipin. Thus rabbit myocardium contains multiple subforms of soluble phospholipase C that differ substantially in surface charge, molecular mass, and sensitivity to cardiolipin. Anionic phospholipids may be important determinants of intracellular distribution of phospholipase C in myocardial tissue.
Wolf
R A
RA
Department of Medicine, Washington University School of Medicine, St. Louis, Missouri 63110.
D000818:Animals; D001696:Biomechanical Phenomena; D002308:Cardiolipins / Q000494:pharmacology*; D007700:Kinetics; D009206:Myocardium / Q000201:enzymology*; D011817:Rabbits; D012508:Sarcolemma / Q000201:enzymology; D013347:Subcellular Fractions / Q000201:enzymology*; D010738:Type C Phospholipases / Q000378:metabolism*
D002308:Cardiolipins; D010738:Type C Phospholipases