Lipids and lipolytic enzyme activities of rat heart mitochondria |
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Authors: | J W Palmer P C Schmid D R Pfeiffer H H Schmid |
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Institution: | The Hormel Institute, University of Minnesota, Austin, Minnesota 55912 USA |
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Abstract: | The lipid composition and lipolytic enzyme activities in rat cardiac mitochondria were examined. Subsarcolemmal mitochondria were prepared by treatment of heart muscle with a Polytron tissue processor, while interfibrillar mitochondria were released by exposure of the remaining low-speed pellet to the protease, nagarse. These procedures are known to yield two functionally different populations of mitochondria. However, their phospholipid contents and compositions were identical, as were the positional distributions of the constituent fatty acids. Of the ethanolamine phospholipids, 20% were plasmalogens, and about 2% of the choline phospholipids consisted of this alkenylacyl species. Both subsarcolemmal and interfibrillar mitochondria contained a Ca2+-activated phospholipase A2, as evidenced by the Ca2+-dependent release of unsaturated fatty acids and lysophosphatidylethanolamine from endogenous lipids. Ruthenium red prevented the activation of this enzyme by Ca2+, indicating that the activity is located in the matrix space or associated with the inner surface of the inner membrane. Both mitochondrial fractions produced free fatty acids and lysophosphatidylethanolamine in the absence of free Ca2+ apparently due to an outer membrane phospholipase A1. The activity of this enzyme decreased with time, particularly in interfibrillar mitochondria, providing that Ca2+ was absent. Nagarse treatment of subsarcolemmal mitochondria resulted in a preparation with the same phospholipase A1 properties as interfibrillar mitochondria. The possibility that differences in phospholipase A1 properties account for some of the functional variations between the two mitochondrial types is discussed. |
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