UDPgalactose:glycoprotein galactosyltransferase (EC 2.4.1.-) activity was demonstrated in homogenates from whole rat brain, isolated neuromal perikarya, enriched glial cell fractions, and cultured rat glial tumor cells (clone C6). 2. Galactosyltransferase activity was enriched 3-9-fold in neuronal perikarya and 1.4--1.8-fold in the glial cell fraction over the activity in whole brains from 19- and 40-day-old rats. The activity of galactosyltransferase in neuronal perikarya decreased with age. Extensive contamination of the glial cell fraction with membranous fragments appeared to obscure the precise specific activity of this fraction. 3. The specific activity of the enzyme in glial tumor cells was 4--8-fold higher than in brain tissue when the enzyme was assayed under identical conditions using endogenous and different exogenous acceptors. 4. Galactosyltransferase activities from adult brain and glial tumor cells had similar properties. They both required Mn-2 plus and Triton, and exhibited pH optima between 5 and 7. The apparent Km of the enzyme for UDPgalactose was 1.3-10-minus 4 M for brain tissue and 2.2-10-minus 4 M for glial tumor cells. 5. The high galactosyltransferase activity in glial tumor cells and in neuronal perikarya of younger rats is compatible with the possibility of a role of this enzyme in developing brain.
