Decreased in vivo protein and phospholipid methylation after in vivo elevation of brain S-adenosyl-homocysteine.

The administration of adenosine together with homocysteine resulted in a dose-related elevation of cerebral S-adenosyl-Lhomocysteine without concomitant perturbation of S-adenosyl-Lmethionine levels. The adenosine + homocysteine treatment also decreased the incorporation of labjle and stable methyl groups into brain protrjins. Brain [ HI-phosphatidyl N,N-dimethylethanolamine and [ HI-phgsphatidylcholine were also significantly decreased while [ HI-phosphatidyl-N-monomethylethanolamine remained unchanged. The data indicate that elevated brain S-adenosylhomocysteine can markedly and selectively inhibit the in vivo methylation of brain proteins and phospholipids.