DISTRIBUTION OF FOLIC ACID COENZYMES AND FOLATE DEPENDENT ENZYMES IN MOUSE BRAIN

—Folic acid coenzymes were found to be distributed equally between post-nuclear particulate and soluble fractions from whole Swiss mouse brain. Mitochondria isolated from the particulate fraction contained essentially only the N5-methyl derivative of folate, virtually all of which was in a polyglutamate form. Isolated synaptosomes contained significantly more folate than did mitochondria, with the greater proportion being non-N5-methyl derivatives. Osmotic lysis of synaptosomes released only a small portion of the folate; approximately 80 per cent remained with the particulate components of the synaptosome. The enzymes serine transhydroxymethylase and N5, N10-methylenetetrahydrofolate dehydrogenase were found in both the soluble and particulate fractions while formiminoglutamic acid:tetrahydrofolate formiminotransferase activity could not be detected. These findings may be of importance with respect to the synaptic functions of folate coenzymes, including the methylation of biogenic amines.