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Properties of Particulate and Detergent‐Solubilized Phospholipid N ‐Methyltransferase Activity from Calf Brain
Author(s) -
Percy A. K.,
Moore J. F.,
Waechter C. J.
Publication year - 1982
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1982.tb07919.x
Subject(s) - chemistry , phospholipid , phosphatidylcholine , membrane , enzyme , biochemistry , methyltransferase , divalent , chromatography , methylation , organic chemistry , gene
Calf brain membranes catalyze the enzymatic transfer of [CH 3 ‐ 3 H]methyl groups from S‐adenosyl‐ l ‐[CH 3 ‐ 3 H]methionine into endogenous phosphatidyl‐ N ‐methylethanolamine (PME), phosphatidyl‐ N,N ‐dimethylethanolamine (PDE), and phosphatidylcholine (PC). Phospholipid N ‐methylation can be stimulated by the addition of exogenous PME or PDE, added in aqueous dispersions with sodium taurocholate. When membranes are incubated in the presence of exogenous PME, [CH 3 ‐ 3 H]PDE represents 86% of the labeled phospholipid products. When exogenous PME is replaced by PDE, 91% of the label is incorporated into PC. Thus, under these in vitro conditions it is possible to assay PME‐ and PDE‐ N ‐methyitransferase activity separately. The calf brain phospholipid N ‐methyltransferase activity has also been solubilized by treating the membranes ultrasonically in the presence of Triton X‐100 and 10 m M monothioglycerol. When the detergent extracts are incubated in the presence of exogenous PME, [CH 3 ‐ 3 H]PDE represents 86% of the enzymatically labeled products. In the presence of exogenous PDE, more than 97% of the label is incorporated into PC. Optimal conditions for the membrane‐bound and detergent‐solubilized PME‐ and PDE‐ N ‐methyltransferase activity have been established. These conditions have been used as a basis for testing the hypothesis that the conversion of PME to PC is catalyzed by a single enzyme in calf brain. In these studies, PME‐ and PDE‐ N ‐methyltransferase activities have been found to be similar, if not identical, with respect to: (1) extractability with Triton X‐100; (2) pH optimum; (3) response to divalent cations; (4) apparent K m , for S‐adenosyl‐ l ‐methionine and K I for S‐adenosyl‐ l ‐homocysteine, (5) sensitivity to N ‐ethylmaleimide; and (6) thermal inactivation at 55°. Overall, these results are consistent with the conclusion that in calf brain, PME and PDE are methylated by the same enzyme or by two phospholipid N ‐methyltransferases having very similar properties.