Consequences of the inhibition of cardiolipin metabolism in Haemophilus parainfluenzae

Examination of phospholipid metabolism in Haemophilus parainfluenzae with inhibitors of various cellular functions indicated that macromolecular synthesis and lipid metabolism can be dissociated at least for a short time. Two classes of inhibitors have relatively specific effects on cardiolipin (CL) metabolism. Pentachlorophenol and p-hydroxymercuribenzoate blocked CL synthesis but allowed CL hydrolysis to phosphatidic acid and phosphatidyl glycerol (PG); 3,3',4,5'-tetrachlorosalicylanilide (TCS) and carbonyl cyanide m-chlorophenylhydrazone (m-CCCP) blocked CL hydrolysis with the stoichiometric accumulation of CL. It appeared as if TCS and m-CCCP inhibited a vital activity coupled with the hydrolysis of CL by the highly active, CL-specific phospholipase D found in this organism. Because TCS and m-CCCP are thought to act by destroying the proton gradient thereby interrupting energy-dependent transport, it is possible that a highly active portion of the cellular CL could be coupled to some phase of this process.

Cardiolipin-specific phospholipase D of Haemophilus parainfluenzae. II. Characteristics and possible significance

A phospholipase specific for cardiolipin (CL) was found in the membrane of Haemophilus parainfluenzae. The enzyme hydrolyzed CL to phosphatidic acid (PA) and phosphatidylglycerol (PG), indicating that it was a phospholipase D (an enzyme activity believed to be confined to higher plants). In addition to its substrate specificity, this enzyme was unusual in its requirement for Mg(2+) (K(m) of 1.3 mm) for maximal activity and its inhibition by chelating agents, heavy metals, some detergents, and organic solvents. When inhibitors of phospholipase activity were added to the growth medium, CL accumulated and PG disappeared in the membrane, suggesting that the phospholipase D was active in vivo. The activity of phospholipase D in cell-free homogenates was greater than expected from earlier studies of CL metabolism and greater than the other phospholipase activities detected in the homogenate. The high activity of the CL-specific phospholipase D suggests there might be a very active degradation of CL to PG and PA and an active resynthesis of CL from the hydrolysis products.