Electrophoretic analysis of the major polypeptides of the human erythrocyte membrane.

A fluid mosaic model is presented for the gross organization and structure of the proteins and lipids of biological membranes. The model is consistent with the restrictions imposed by thermodynamics. In this model, the proteins that are integral to the membrane are a heterogeneous set of globular molecules, each arranged in an amphipathic structure, that is, with the ionic and highly polar groups protruding from the membrane into the aqueous phase, and the nonpolar groups largely buried in the hydrophobic interior of the membrane. These globular molecules are partially embedded in a matrix of phospholipid. The bulk of the phospholipid is organized as a discontinuous, fluid bilayer, although a small fraction of the lipid may interact specifically with the membrane proteins. The fluid mosaic structure is therefore formally analogous to a two-dimensional oriented solution of integral proteins (or lipoproteins) in the viscous phospholipid bilayer solvent. Recent experiments with a wide variety of techniqes and several different membrane systems are described, all of which abet consistent with, and add much detail to, the fluid mosaic model. It therefore seems appropriate to suggest possible mechanisms for various membrane functions and membrane-mediated phenomena in the light of the model. As examples, experimentally testable mechanisms are suggested for cell surface changes in malignant transformation, and for cooperative effects exhibited in the interactions of membranes with some specific ligands. Note added in proof: Since this article was written, we have obtained electron microscopic evidence (69) that the concanavalin A binding sites on the membranes of SV40 virus-transformed mouse fibroblasts (3T3 cells) are more clustered than the sites on the membranes of normal cells, as predicted by the hypothesis represented in Fig. 7B. T-here has also appeared a study by Taylor et al. (70) showing the remarkable effects produced on lymphocytes by the addition of antibodies directed to their surface immunoglobulin molecules. The antibodies induce a redistribution and pinocytosis of these surface immunoglobulins, so that within about 30 minutes at 37 degrees C the surface immunoglobulins are completely swept out of the membrane. These effects do not occur, however, if the bivalent antibodies are replaced by their univalent Fab fragments or if the antibody experiments are carried out at 0 degrees C instead of 37 degrees C. These and related results strongly indicate that the bivalent antibodies produce an aggregation of the surface immunoglobulin molecules in the plane of the membrane, which can occur only if the immunoglobulin molecules are free to diffuse in the membrane. This aggregation then appears to trigger off the pinocytosis of the membrane components by some unknown mechanism. Such membrane transformations may be of crucial importance in the induction of an antibody response to an antigen, as well as iv other processes of cell differentiation.

The fluid mosaic model of the structure of cell membranes.

It is proposed that most neoplasms arise from a single cell of origin, and tumor progression results from acquired genetic variability within the original clone allowing sequential selection of more aggressive sublines. Tumor cell populations are apparently more genetically unstable than normal cells, perhaps from activation of specific gene loci in the neoplasm, continued presence of carcinogen, or even nutritional deficiencies within the tumor. The acquired genetic insta0ility and associated selection process, most readily recognized cytogenetically, results in advanced human malignancies being highly individual karyotypically and biologically. Hence, each patient's cancer may require individual specific therapy, and even this may be thwarted by emergence of a genetically variant subline resistant to the treatment. More research should be directed toward understanding and controlling the evolutionary process in tumors before it reaches the late stage usually seen in clinical cancer.

http://science.sciencemag.org/content/sci/194/4260/23.full.pdf

The clonal evolution of tumor cell populations

A surface glycoprotein modulating drug permeability in Chinese hamster ovary cell mutants.

I read this book the same weekend that the Packers took on the Rams, and the experience of the latter event, obviously, colored my judgment. Although I abhor anything that smacks of being a handbook (like, \"How to Earn a Merit Badge in Neurosurgery\") because too many volumes in biomedical science already evince a boyscout-like approach, I must confess that parts of this volume are fast, scholarly, and significant, with certain reservations. I like parts of this well-illustrated book because Dr. Sj6strand, without so stating, develops certain subjects on technique in relation to the acquisition of judgment and sophistication. And this is important! So, given that the author (like all of us) is somewhat deficient in some areas, and biased in others, the book is still valuable if the uninitiated reader swallows it in a general fashion, realizing full well that what will be required from the reader is a modulation to fit his vision, propreception, adaptation and response, and the kind of problem he is undertaking. A major deficiency of this book is revealed by comparison of its use of physics and of chemistry to provide understanding and background for the application of high resolution electron microscopy to problems in biology. Since the volume is keyed to high resolution electron microscopy, which is a sophisticated form of structural analysis, but really morphology in a modern guise, the physical and mechanical background of The instrument and its ancillary tools are simply and well presented. The potential use of chemical or cytochemical information as it relates to biological fine structure , however, is quite deficient. I wonder when even sophisticated morphol-ogists will consider fixation a reaction and not a technique; only then will the fundamentals become self-evident and predictable and this sine qua flon will become less mystical. Staining reactions (the most inadequate chapter) ought to be something more than a technique to selectively enhance contrast of morphological elements; it ought to give the structural addresses of some of the chemical residents of cell components. Is it pertinent that auto-radiography gets singled out for more complete coverage than other significant aspects of cytochemistry by a high resolution microscopist, when it has a built-in minimal error of 1,000 A in standard practice? I don't mean to blind-side (in strict football terminology) Dr. Sj6strand's efforts for what is \"routinely used in our laboratory\"; what is done is usually well done. It's just that …

Methods in Enzymology.

Preparation and properties of plasma membrane and endoplasmic reticulum fragments from isolated rat fat cells.

Plasma membranes purified from human red cells were Converted into small vesicleS by disruption in alkaline buffer of low ionic strength. Most of these vesicles were inside-out. The presence of divalent cations prevented this inversion. The inside-out vesicles were separatcd from right-side-out vesicles by centrifugration to equilibrium in dextran density gradients.

https://science.sciencemag.org/content/sci/168/3928/255.full.pdf

Inside-Out Red Cell Membrane Vesicles: Preparation and Purification

Disposition of the major proteins in the isolated erythrocyte membrane. Proteolytic dissection.

which were 10% higher than that obtained by the Lowry method. One mg of membrane "protein" corresponds to about 1.5 mg dry weight, most of the nonprotein mass consisting of phosphatides and cholesterol. About 1.5% of the dry mass is carbohydrate and 1-2% is contributed by tightly bound RNA. It should be noted that cellular membranes obtained in isoosmotic media (e.g., 0.25 M sucrose) ordinarily contain considerable quantities of trapped, soluble proteins,8 but in the isolation procedure here employed, these contaminants were removed by "osmotic shock."'24 The reported optical measurements are thus due to components integral with the membrane structure. 2-Chloroethanol (Eastman White Label) was completely transparent to 260 m,u after fractional redistillation. The apparent pH of 9:1 2-chloroethanol:water was about 1.1. Lysolecithin (Sigma Chemical Co.) was used at a concentration of 0.13 mg/ml which reduced the turbidity of PM suspensions by 50%. Infrared spectra: A Perkin-Elmer spectrophotometer model 521 was employed. Solid films were prepared by applying about 0.5 mg membrane protein (in aqueous suspension, or chloroethanol or formic acid solution) as a 0.5 X 2-cm band in the center of the silver chloride plate and drying in air at about 25?C. Once dried, the films were strongly adherent to the plate. Quantitative extraction of lipids from the films was achieved by immersing the plates in 2:1 chloroform:methanol (v:v) for 20 min at room temperature. After rinsing with the same solvent, the films were dried in air. To acidify the films, the dried plates were immersed for 20 min in 0.001-0.1 N HCI at room temperature, rinsed with distilled water, and air-dried. In order to have the films located reproducibly in the optical path, all manipulations of the films were performed with the plates in their plate-holders.

Donald F. H. Wallach

Papers

Electrophoretic analysis of the major polypeptides of the human erythrocyte membrane.

Preparation and properties of plasma membrane and endoplasmic reticulum fragments from isolated rat fat cells.

Inside-Out Red Cell Membrane Vesicles: Preparation and Purification

Disposition of the major proteins in the isolated erythrocyte membrane. Proteolytic dissection.

Protein conformations in cellular membranes.