Incorporation of Intracisternally Administered l‐[methyl‐³H]Methionine and S‐Adenosyl‐l‐[methyl‐³H]‐Methionine into Rat Brain Phospholipids

Abstract

The incorporation of intracisternally injected L-[methyl-3H]methionine [( 3H]Met) or S-adenosyl-L-[methyl-3H]methionine (Ado[3H]Met) into rat brain AdoMet and phospholipid pools was examined. When [3H]Met was administered, both AdoMet and phospholipid pools were labeled. However, exogenously injected Ado[3H]Met did not serve as a substrate for phospholipid-N-methyltransferases. It was concluded that only Ado[3H]Met formed in situ was utilized to methylate phospholipids and that this process was initiated on the cytoplasmic side of the membrane. The apparent biological half-life in brainstem of phosphatidyl-N-monomethylethanolamine and phosphatidyl-N,N-dimethylethanolamine formed from [3H]Met was 1.4 and 1.7 days, respectively. The half-life of phosphatidylcholine could not be determined due to interference from peripheral sources.

Molecular composition of the phosphatidylcholines produced by the phospholipid methylation pathway in rat brain in vivo

“…The third pathway, that involving phospholipid methylation (Bremer & Greenberg, 1960) which makes PC by three sequential methylations of phosphatidylethanolamine (PE), is the only known pathway capable of generating choline moieties de novo. Brain PC has been shown to be produced via PE methylation both in vivo (Chida & Arakawa, 1971;Morganstern & Abdel-Latif, 1974;Zawad & Brown, 1985) and in vitro by various subcellular fractions (Blusztajn et al, 1979;Crews et al, 1980); this pathway has also been identified in neuronal and glial cell cultures (Strittmatter et al, 1979;Dainous et al, 1982;Yavin, 1985).…”