Journal of Lipid Research, Vol. 10, 411-420, July 1969
Copyright © 1969 by Lipid Research, Inc.

Differentiation of phospholipases A in mitochondria and lysosomes of rat liver

Moseley Waite , G. L. Scherphof , F. M. G. Boshouwers , and L. L. M. Van Deenen

The Bowman Gray School of Medicine of Wake Forest University, Winston-Salem, North Carolina 27103 and The State University of Utrecht, Utrecht, The Netherlands

Highly purified mitochondria from rat liver contain a phospholipase A that catalyzes removal of 2-fatty acids, with a pH optimum above pH 8.0. Lysosomal preparations appeared to have two phospholipases A associated with them, one with a pH optimum at about pH 4.0, the second between pH 6.0 and 7.0.

Mitochondrial phospholipase A hydrolyzed exogenous phospholipid as fast as or faster than endogenous phospholipid. The difference in specific radioactivity of ¹⁴C-ethanolamine-labeled endogenous mitochondrial phospholipid before and after incubation indicates that a fraction of mitochondrial phosphatidyl ethanolamine is hydrolyzed more rapidly than the mitochondrial phospholipids as a whole.

Acyl bond hydrolysis of exogenous and endogenous phospholipid by mitochondria was stimulated by free fatty acid, Ca⁺⁺, or in certain cases, monoacyl phospholipids or by treatments that disrupt the mitochondrial membrane. Of various fatty acids tested, lauric, myristic, oleic, and linoleic were most effective.

ADP and ATP inhibited mitochondrial phospholipase, probably because they compete for Ca⁺⁺. Mg⁺⁺ also behaved as a competitive inhibitor; the effect was overcome by relatively little Ca⁺⁺.

Supplementary key words pH optima • fatty acid stimulation • Ca⁺⁺ requirement • inhibition by ATP, ADP, and Mg⁺⁺ • endogenous vs. exogenous phospholipid hydrolysis • mitochondrial membrane

Submitted on October 9, 1968
Accepted on March 10, 1969

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