Method of visualization of matrix-bound proteins. Leucine aminopeptidase bound to Sepharose and Sephadex beads

On the role of microfilaments in cell-shape-mediated growth control of lens epithelial cells

With regard to the fact that, in anchorage-dependent lens epithelial cells, DNA synthesis can be switched on and off by cell flattening and cell rounding, respectively, the state of the microfilaments has been followed by labelling actin with FL-phalloidin during cell-shape alterations. Cell flattening proved to be accompanied by both a structural organization of actin filaments into stress fibres and an enlargement of the area of the cell nucleus. Cell rounding, on the other hand, caused the microfilament bundles to disappear and the area of the nucleus to become smaller. From the time course of the inhibition of DNA synthesis by cytochalasin B, it was inferred that functionally intact microfilaments are required for the entrance of the cells into DNA synthesis but not for the maintenance of ongoing DNA synthesis. The assumption has been made that the tension, generated by microfilaments during cell spreading, will affect the state of the plasma membrane as well as the shape and the structure of the nucleus, which in turn seems to be preparatory for cells to enter the cycle.

An experimental verification of the theory of diffusion limitation of immobilized enzymes

Alkaline phosphatase (orthophosphoric-monoester phosphohydrolase (alkaline optimum), EC 3.1.3.1) was covalently bound to Sepharose beads. Kinetic measurements with the substrate p-nitrophenyl phosphate gave the following results. Effectiveness factors were decreasing with increasing bound activity, decreasing substrate concentration, and increasing particle radius of the beads. With decreasing effectiveness factors, the apparent Michaelis constants were decreasing. Preparations with high bound activities did not obey Michaelis-Menten kinetics at substrate concentrations much higher than the apparent Michaelis constants. The experimental results accorded quantitatively with the theory of diffusion limitation (Engasser, J.M. (1978) Biochim. Biophys. Acta 526, 301-310).

Studies of the distribution of proteins bound to CNBr-activated Sepharose 6B at the electron-microscopic level

Proteins were covalently attached to Sepharose by the CNBr method. Their distribution across the carrier beads was studied at the electron microscopic level. The approach has been to ferritinstain and to section the gel beads. Ferritin was either coupled directly to the polysaccharide backbone of the carrier or conjugated with pure rabbit anti-aminopeptidase in order to visualize covalently bound leucine aminopeptidase by the immunferritin technique. The results corroborate earlier fluorescence microscopic findings of a uniform protein distribution, provided that a number of conditions are fulfilled.