Subcellular localization of the phospholipases A of XXXX heart: evidence for a cytosolic phospholipase A1.

@entity52765 @entity6579 @entity741 @entity35 @entity36316 @entity14146
During @entity741 increased levels of lysoglycerophospholipids have been reported which may be deleterious to myocardial function. Phospholipases are presumed to be important in the regulation of this process. To further quantify and characterize the activity of heart phospholipases, we carried out a systematic analysis of @entity36316 activity in @entity35 heart subcellular fractions isolated by the method of Palmer et al. (J. Biol. Chem. 1972. 262: 8731-8739). Neutral @entity36316 was recovered predominately in the cytosolic (soluble) fraction which represented 46% of recovered activity, while the microsomal and subsarcolemmal mitochondrial fractions represented 15% and 12% of the total recovered activity, respectively. Cytosolic @entity36316 differed from the two principal membrane-bound phospholipases A in its pH dependence and apparent Km for substrate. The cytosolic enzyme had a Km (apparent) for @entity14146 of 0.07 mM versus 0.28-0.33 mM for the membrane-associated phospholipases A. Acid @entity36316 activity had a subcellular distribution consistent with a lysosomal localization. @entity52765 was found principally in the cytosolic, microsomal, and the subsarcolemmal and interfibrillar mitochondrial fractions where it represented 46, 17, 6.3, and 6.9% of the recovered activity, respectively. The positional specificity of the respective phospholipases was assessed. This analysis was complicated by the fact that in heart, @entity52765 has an observed Vmax 3.6- to 4.5-fold greater than that of @entity36316 in the various subcellular fractions. Equations were derived to obtain corrected values for the activity of phospholipases A1 and A2. Using this method we found that the cytosolic and lysosomal fractions contained phospholipase A1, while the mitochondrial fractions contained primarily phospholipase A2. In heart microsomes, the positional specificity of @entity36316 could not be determined because @entity52765 activity was very high and @entity6579 did not accumulate.
