Lysophosphatidylcholine metabolism in the rabbit heart. Characterization of metabolic pathways and partial purification of myocardial lysophospholipase-transacylase.
Metabolism of lysophosphatidylcholine (LPC), recently implicated in arrhythmogenesis, was characterized in rabbit ventricular homogenates. Activities of four enzymatic pathways were distinguishable after subcellular fractionation and DEAE-Sephacel chromatography including microsomal lysophospholipase, microsomal acyl coenzyme A/LPC acyltransferase, cytosolic lysophospholipase, and cytosolic lysophospholipase-transacylase. Microsomal lysophospholipase activity was attenuated 81% by acidosis comparable to that in ischemic myocardium (pH 6.5) and was inhibited by substrate. LPC acyltransferase was identified in the microsomal fraction based on CoA-dependent phosphatidyl choline synthesis, the positional specificity of acylation of LPC, and identical reaction velocities with both of its labeled co-substrates. LPC acyltransferase had a Vmax of 5.1 nmol/mg/min, a broad pH optimum centered at pH 7, and an apparent Km for LPC and palmitoyl-CoA of 14 microM and 7 microM. Cytosolic lysophospholipase was separated from lysophospholipase-transacylase by DEAE-Sephacel chromatography and distinguished from microsomal lysophospholipase by its broad pH activity curve, Michaelis-Menten kinetics (Vmax = 9.5 nmol/mg/min, Km = 7.5 microM), and lack of substrate inhibition. Lysophospholipase-transacylase was identified in the cytosolic fraction by CoA-independent phosphatidyl choline synthesis and purified 4885-fold from homogenate by ammonium sulfate precipitation, DEAE-Sephacel, hydroxylapatite, gel filtration, and polylysine chromatography. The partially purified enzyme had a transacylase/lysophospholipase activity ratio of 0.6, and transacylation of LPC was prominent at submicellar concentrations of substrate.
D000217:Acyltransferases / Q000302:isolation & purification / Q000378:metabolism*; D000818:Animals; D003600:Cytosol / Q000201:enzymology; D007700:Kinetics; D008244:Lysophosphatidylcholines / Q000378:metabolism*; D008245:Lysophospholipase / Q000302:isolation & purification / Q000378:metabolism*; D008861:Microsomes / Q000201:enzymology; D008929:Mitochondria, Heart / Q000201:enzymology; D009097:Multienzyme Complexes / Q000302:isolation & purification / Q000378:metabolism*; D009206:Myocardium / Q000201:enzymology*; D010740:Phospholipases / Q000378:metabolism*; D011817:Rabbits; D013379:Substrate Specificity
D008244:Lysophosphatidylcholines; D009097:Multienzyme Complexes; D000217:Acyltransferases; D010740:Phospholipases; D008245:Lysophospholipase; C021782:lysophospholipase-transacylase