Enzymatic properties of phospholipid methylation in rabbit platelets.
The enzymatic properties of phospholipid methylation in rabbit platelets were examined using S-adenosyl-L-[methyl-3H]methionine as a substrate. pH optimum for the methylation was around 10.5 under Tris-HCl and glycine-NaOH buffer systems. When Tris-HCl buffer was replaced by phosphate buffer, pH optimum shifted to around 8.0 and the methylation was increased approximately threefold, compared with that in the case of Tris-HCl buffer at pH 8.0. The formation of the 3H-methylated phospholipids was increased by addition of exogenous phosphatidyl-N-monomethylethanolamine or phosphatidyl-N,N-dimethylethanolamine, intermediates of the biosynthesis of phosphatidylcholine from phosphatidylethanolamine. However, the increase in product formations by addition of exogenous intermediates was all but equal under Tris-HCl and phosphate buffer systems at pH 8.0. These results suggest that phosphate ion stimulates the first step of the successive methylation to form phosphatidyl-N-monomethylethanolamine from phosphatidylethanolamine. The methylation in platelets was inhibited to 30% of the basal value with Ca2+ (0.2 mM). However, Ca2+ showed different effects on the methylation in various tissues (activation to 150% of the basal value in the adrenal gland and slight inhibition to 82-88% of corresponding basal values in the liver, lung, kidney and brain).
D000818:Animals; D001792:Blood Platelets / Q000187:drug effects / Q000201:enzymology* / Q000378:metabolism; D002021:Buffers; D002118:Calcium / Q000494:pharmacology / Q000502:physiology; D002413:Cations, Divalent / Q000494:pharmacology; D002855:Chromatography, Thin Layer; D006863:Hydrogen-Ion Concentration; D008745:Methylation; D008780:Methyltransferases / Q000097:blood*; D010713:Phosphatidylcholines / Q000096:biosynthesis; D010714:Phosphatidylethanolamines / Q000378:metabolism / Q000494:pharmacology; D010743:Phospholipids / Q000097:blood*; D011817:Rabbits; D012436:S-Adenosylmethionine / Q000031:analogs & derivatives / Q000378:metabolism
D002021:Buffers; D002413:Cations, Divalent; D010713:Phosphatidylcholines; D010714:Phosphatidylethanolamines; D010743:Phospholipids; C032000:phosphatidyl-N-monomethylaminoethanol; C026508:phosphatidyldimethylethanolamine; C016207:S-adenosyl-2-methylmethionine; D012436:S-Adenosylmethionine; D008780:Methyltransferases; D002118:Calcium