Cell plasma membrane external surface glycosyltransferases: activity in the cell mitotic cycle

Purification of plasma membrane of guinea pig peritoneal macrophages

A method using sucrose density gradient centrifugation is described for the purification of plasma membrane of guinea pig peritoneal exudate macrophages. Assays for composition and for marker enzyme activities have been modified for use with the small amounts of subcellular macrophage material. The plasma membrane was obtained in 57% yield and contained 7% of the protein. The purified plasma membrane fraction is five-fold enriched in phospholipid to protein ratio and contains no contaminating DNA, none of the cytoplasmic marker lactate dehydrogenase, no detectable mitochondrial contamination and a low contamination with lysosomal enzymes (7%). Purified plasma membrane containing 4 mg of protein can be prepared from 1 ml of pelleted macrophages in a one-day operation.

Properties and subcellular localization of CMP-N-acetylneuraminic acid hydrolase of calf kidney

The properties and subcellular distribution of CMP-N-acetylneuraminic acid (CMP-NAcNeu) hydrolase were studied in the cortex of calf kidney. The pH optimum was 9.0 in both Tris - HCl and glycine/NaOH buffer. The apparent Km was 0.47 mM and the apparent V 15.3 mumol/h/g wet wt of calf kidney cortex. A stimulation by divalent metal ions (Ca2+ and Mg2+) was demonstrated for the hydrolase. In the presence of Triton X-100 an increase in enzyme activity was observed. CMP-NAcNeu hydrolase was inhibited by EDTA, beta-mercaptoethanol, nucleoside phosphates and nucleotide-sugars. The inhibition was more pronounced when a sub-optimal CMP-NAcNeu concentration was used. The enzyme appeared to be localized in the plasma membranes. In the plasma membrane preparation of calf kidney cortex, which was derived mainly from the proximal tubule cells, the yield of CMP-NAcNeu hydrolase (13%) and its increase in specific activity (9-fold) was as high as for the plasma membrane marker enzymes. From subcellular distribution studies it appeared that the enzyme was localized mainly at the bursh border side of the plasma membrane of the proximal tubule cell.

Cell surface galactosyltransferase and lectin agglutination of thymus and spleen lymphocytes

Lectin agglutination and cell surface galactosyltransferase (EC 2.4.1.67; 1-O-alpha-D-galactosyl-myo-inositol:raffinose galactosyltransferase) enzyme activity have been studied with thymus and spleen lymphocytes of neonatal rats. Thymus lymphocytes were more agglutinable by concanavalin A than by wheat germ agglutinin, whereas spleen lymphocytes were more agglutinable by wheat germ agglutinin than by concanavalin A. Thymus lymphocytes, but not spleen lymphocytes, of neonatal rats could be blast transformed by concanavalin A. Cell surface galactosyltransferase activity was present on both types of lymphocytes, but was greatly increased on thymus cells after blast transformation. The differences in lectin agglutination suggest a difference in the surface membranes of thymus and spleen lymphocytes. The increase in cell surface galactosyltransferase activity with blast transformation of thymus lymphocytes may be related to the exteriorization of the Golgi apparatus into the plasma membrane.