AJP - Cell Physiology, Vol 257, Issue 5 C926-C935, Copyright © 1989 by American Physiological Society
Cardiolipin-sensitive phospholipase C in subcellular fractions of rabbit myocardium
R. A. Wolf
Department of Medicine, Washington University School of Medicine, St. Louis, Missouri 63110.
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.
