Leonard Warren

Glycopeptides from the Surface of Control and Virus-Transformed Cells

Glycopeptides were removed by trypsin digestion from the surface of control cells and cells transformed by Rous sarcoma virus, murine sarcoma virus, or polyoma virus. After digestion with pronase, the glycopeptides were analyzed by gel filtration. The elution profiles suggest that there are differences in the glycopeptides from the surface of control cells and those from transformed cells.

Chapter 7 The Biological Significance of Turnover of The Surface Membrane of Animal Cells

Publisher Summary This chapter examines the flux that occurs in the components of the surface membrane of animal cells, insofar as they are known and speculates on the possible relevance of this phenomenon to cellular behavior. It attempts to construct a hypothesis that affords some explanation of certain aspects of cellular behavior, both social and metabolic. It begins with the notion that the cell in culture synthesizes almost as much surface membrane material in the dividing and nondividing state. When dividing, the new material goes into the making of a new cell with a small amount of turnover; when not dividing, the material goes into the cell structure and an equivalent amount is rejected and there is a high rate of turnover. If the surface structure is damaged, it is replaced in the course of turnover at the same rate that it would have been if it had not been damaged. The chapter presents an oversimplified hypothesis on the basis of the manifestation of malignancy. The difference in turnover rates of the surface membrane of dividing and nondividing cells could be reflected in differences in virus receptivity, antigenic specificity, adhesiveness, permeability, and electrical coupling.

Removal of sodium dodecyl sulfate from proteins.

Abstract A convenient and relatively simple electrodialysis method for the removal of sodium dodecyl sulfate (SDS) from proteins is described. Six samples can be processed simultaneously. The kinetics of removal of SDS from proteins by equilibrium dialysis and electrodialysis have been studied.

Membranes of animal cells. VII. Carbohydrates of surface membranes and whole cells

Abstract The carbohydrate content of mouse fibroblasts (L cells) and surface membranes was examined. The amount of sialic acid in intact cells was found to vary. A portion of this variation could be related statistically to change in protein content of the cell. Some of the variation correlated with the growth rate of the culture, slower growing cultures containing higher amounts of sialic acid. The surface membranes were rich in most monosaccharides relative to the rest of the cell. Although considerable variation in the sialic acid and other monosaccharides was observed, some of the monosaccharides appeared to have a fairly constant molar ratio, one to the other. The results suggest that the glycoproteins and/or glycolipids of the intact L cell and surface membrane are quite variable. Studies with neuraminidase indicated that 25–35% of the sialic acid of the surface membranes was resistant to cleavage by the enzyme under the conditions employed. The amount of sialic acid released from the whole cells indicated that neuraminidase probably entered the cells during the incubation period.

Membranes of animal cells. VIII. Distribution of sialic acid, hexosamines and sialidase in the L cell

Abstract The distribution of sialic acid and hexosamines was studied in purified organelles obtained from L cells. The major portion of the sialic acid of the intact cell is found in the surface membranes (66%). Only small amounts of sialic acid are found in the other purified fractions with the exception of the lysosomes which contained approx. 16%. The hexosamines are largely distributed between the surface membranes (33%) and soluble fraction (25%). Microsomes and mitochondria contain 14 and 11%, respectively, of the hexosamines of the intact cell and the nuclei contain 4%. The molar ratio of hexosamines to sialic acid of these fractions indicate differences in glycoprotein and/or glycolipid contents of the cell organelles. Some sialidase ( N- acetylneuraminate glycohydrolase , EC 3.2.1.18) activity is present in all of the cell fractions which were examined. However, upon further purification only the lysosomes show an increased specific activity of the enzyme. A procedure is reported for obtaining purified nuclei with the outer nuclear membrane morphologically intact.

The Isolation of the Surface Membranes of Animal Cells: A Survey

At present we are witnessing a rapidly growing interest in the cell surface structure. While some investigators are examining the essential nature of the membrane itself, others, such as virologists, developmental biologists, immunologists, and oncologists are studying the role of the surface membrane in processes relevant to their special interests. Although surface structure of the intact cell can be profitably studied in situ,invaluable information can often be obtained only after removal of the surface structure from the cells. It should be remembered, however, that the vigorous methods employed to remove the structure from the cell and to separate it from other cellular components may alter the membrane; i.e., there may be losses, additions by adsorptive processes, or enzymatic degradation of membrane components and even significant changes of protein configuration. Therefore, use of the isolated membrane should be approached with caution.

Isolation and Properties of Natural Membranes

External and internal cell membranes serve to compartmentalize regions in which optimal conditions can be maintained for discrete functions. The membranes also provide routes of transport for materials and information between and within cells. Techniques that have been devised to permit study of the various membrane activities, and the knowledge acquired by these methods, are described.

An assay for free l-fucose in the presence of the bound sugar

Abstract An assay for free l -fucose in the presence of the bound form is described. It is based upon the enzymatic conversion of free l -fucose to l -fuculose which is measured by the cysteine-carbazole reaction. The assay is sensitive, relatively specific, and is well suited for the measurement of fucosidases.