RESUMO
The catalysis by phosphatidylethanolamine methyltransferase (PEMT) of phosphatidylcholine (PC) synthesis by the successive methylation of phosphatidylethanolamine in the presence of S-adenosylmethionine (AdoMet) as methyl donor, was detected in actively myelinating mouse brains. PEMT activity in the microsome fraction of fetal mouse brain at 17 days of gestation was 253 mu u/mg protein and that of adult brain after 7 days of remyelination following 6 weeks cuprizone administration was 148 mu u/mg. These figures are much higher than found in normal adult brains (1.7 mu u/mg). An increase in PEMT activity was observed in the brains of genetically transmitted diabetic mice, C57BL/KsJ-db/db, and streptozotocin-induced diabetic mice; 16.3 and 9.2 mu u/mg, respectively. The methyl group of mecobalamin was transferred to homocysteine producing AdoMet and was further metabolized into choline and acetylcholine in brain slices. These results suggest that in the diabetic state, an increase in PC synthesis is probably required in order to replace damaged myelin or to supply choline or acetylcholine essential to for nerve functions. Mecobalamin might serve as the source of the methyl group utilized for PC synthesis.
