INVOLVEMENT OF FOLIC-ACID IN THE SYNTHESIS OF MEMBRANE-ASSOCIATED NUCLEOTIDE SUGARS BY NORMAL AND TRANSFORMED MOUSE FIBROBLASTS

A plasma-membrane-containing fraction isolated from Swiss mouse (3T3) fibroblasts was found to contain uridine diphosphate sugars and methyl -uridine diphosphate (mUDP) sugars. The synthesis of the mUDP sugars b y membrane preparations of normal and transformed 3T3 cells occurred f rom the intrinsic membrane uridine-diphosphate sugars + methylene-tetr ahydrofolic acid. Compared to the normal 3T3 cells, the synthesis of m UDP sugars by the transformed 3T3 cells was reduced by 49%. It is prop osed that the plasma-membrane-associated mUDP sugars may be essential for normal cell growth.