Glycoprotein biosynthesis: stimulation of galactose transfer from UDP-( 14 C) galactose into microsomal protein by cytidine 5'-diphosphocholine

Synthesis and secretion of serum phosphorylcholine-binding protein by rat hepatocytes

The incorporation of [1-14C]glucosamine into rat serum phosphorylcholine-binding protein in an isolated rat hepatocyte system was used to demonstrate the synthesis and secretion of this protein by the liver. The hepatocytes after incubating with colchicine resulted in an increased intracellular accumulation of phosphorylcholine-binding protein and less of the synthesized phosphorylcholine-binding protein was secreted into the medium. The synthesis of phosphorylcholine-binding protein was found to be significantly impaired when the hepatocytes were incubated with tunicamycin. The radiolabelled phosphorylcholine-binding protein co-eluted with exogenous phosphorylcholine-binding protein as a homogeneous peak by affinity chromatography. The identity of the radiolabelled phosphorylcholine-binding protein was further established by quantitative immunoprecipitation, polyacrylamide gel electrophoresis and isoelectric focusing.

Udp-galactose: glycoprotein galactosyltransferase activity in a clonal line of rat brain

1. 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.