Molecular biology of cellular membranes with applications to immunology

Binding of the human complement subcomponent C1q to hybrid mouse monoclonal antibodies

Activation of the classical pathway of the complement system is initiated by the binding of C1q to antibody complexes. Here we evaluated the C1q binding capacity of series of monospecific and bispecific hybrid mouse monoclonal antibodies (mAb) and compared them with parental (conventional) mAb. The hierarchy in C1q binding capacity of the bispecific anti-HuIgA1/HRP mAb with homologous H-H chain combinations (IgG2a-2a, IgG2b-2b and IgG1-1) and the parental anti-HuIgA1 or anti-HRP mAb was identical; IgG2a greater than IgG2b much greater than IgG1. Hybrid IgG1-2a mAb bind intermediate amounts of C1q when compared with the IgG1 and IgG2a parental antibodies. IgG1-2b and IgG1-1 hybrid mAb did not bind any C1q, like the IgG1 mAb. We could not observe any difference in C1q binding efficiency between monovalently bound IgG1-2a, IgG2a-2a and IgG2b-2b anti-HuIgA1 HRP mAb and the bivalently bound IgG1-2a, IgG2a-2a and IgG2b-2b anti-HuIgA1 mAb, respectively. Furthermore, these hybrid ms anti-HuIgA1 and bs anti-HRP/HuIgA1 mAb were able to lyse HuIgA1-coated erythrocytes, in the presence of 50% human serum, as efficiently as their parental counterparts. These data indicate that a simultaneous binding of both F(ab') fragment to antigen is not a necessary prerequisite for binding and activation of C1q.

A new radiometric assay for the quantitation of surface-bound IgG on sensitized erythrocytes

We have developed a sensitive, straightforward method for the quantitation of surface-bound IgG on sensitized erythrocytes. The assay is based on the consumption by sensitized cells of anti-IgG antiserum. The remaining anti-IgG is quantitated in a second incubation by precipitation with 125I-IgG in the presence of polyethylene glycol. Calibration curves for this assay were constructed using known amounts of unlabeled IgG. The method can be performed in microtitre plates and eliminates the use of purified anti-erythrocyte antibodies, or highly purified specific anti-IgG antisera. The results were completely consistent with those of immunofluorescence assays, but our method was much more sensitive, less than 500 molecules of IgG per cell being detected reproducibly. The technique is not laborious and takes much less time than previously described methods with similar sensitivity. As an example of the applicability of this test, the implications of ligand density for the detection by EA rosetting of Fc receptors on human monocytes are shown. The results suggest that a large variation exists in the affinity of the different types of Fc receptors for their ligands.

Lysis of nonnucleated red blood cells by cytotoxic T lymphocytes

To establish the role of direct membrane damage in cytotoxic T lymphocytes (CTL)-mediated lysis we investigated whether CTL would be capable of lysing nonnucleated target cells. By antibody-mediated targeting we show that CTL are indeed capable of lysing sheep and human red blood cells.

Alterations in lipid fluidity induced by cholesterol and cholesterol hemisuccinate modulate the organization of microtubule skeletons in epithelial cells

This study was designed to evaluate the role that cholesterol, and the more hydrophilic ester, cholesterol hemisuccinate (CHS) have on the ability of epithelial cells to attach, spread and reorganize microtubule skeletons on a defined substratum. A431 carcinoma cells were grown and incubated with cholesterol, or CHS in polyvinyl pyrrolidone. Subsequently the cells were plated either on plastic petri dishes or plasticware coated with collagen IV or laminin. The alteration in apparent membrane microviscosity was ascertained using fluorescence polarization measurements. Organization of microtubules was determined by immunofluorescence, and by transmission electron microscopy. Cholesterol and CHS inhibited attachment and spreading of epithelial cells. Cells previously attached and spread became spherical after treatment with cholesterol and CHS, but microtubules were unaffected. However, when the cells were pretreated in suspension with cholesterol or CHS the membrane microviscosities markedly increased, and upon subsequent plating those cells adhering neither spread nor organized microtubule skeletons. These results suggest that cholesterol-induced changes in lipid microviscosity modulate the membrane dynamics that control the ability of epithelial cells to attach, spread and organize microtubule skeletons.

Early interactions between animal viruses and the host cell: relevance to viral vaccines

Viral recognition of specific receptors in the host cell plasma membrane is the first step in virus infection. Attachment is followed by a redistribution or capping of virus particles on the cell surface which may play a role in the uptake process. Certain viruses penetrate the plasma membrane directly but many, both enveloped and non-enveloped viruses, are endocytosed at coated pits and subsequently pass into endosomes. The low pH environment of the endosome facilitates passage of the viral genome into the cytoplasm. For some viruses the mechanism of membrane penetration is now known to be linked to a pH-mediated conformational change in external virion proteins. As a consequence of infection there are alterations in the permeability of the plasma membrane which may contribute to cellular damage. Recent advances in the understanding of these processes are reviewed and their relevance to the development of new strategies for vaccines emphasised.

Nucleotide sequence of cDNA and derived amino acid sequence of human complement component C9

The nucleotide sequence coding for the ninth component of human complement (C9) has been determined and the corresponding amino acid sequence has been derived. A human liver cDNA library was screened by the colony-hybridization technique using two radiolabeled oligonucleotide probes that correspond to known regions of the C9 amino acid sequence. Two recombinant plasmids were isolated and their cDNA inserts were sequenced. The derived protein sequence consists of 537 amino acids in a single polypeptide chain. A profile of the hydropathic index versus sequence number indicates that the amino-terminal half of C9 is predominantly hydrophilic in character whereas the carboxyl-terminal section of this protein is more hydrophobic. The amphipathic organization of the primary structure of C9 is consistent with the known potential of polymerized C9 to penetrate lipid bilayers, causing the formation of transmembrane channels.

Some problems associated with radiolabeling surface antigens on helminth parasites: a brief review

Recent developments in technology have facilitated substantial advances in the characterization of surface antigens from a wide variety of both normal and neoplastic cells. However, the immunochemistry of parasites has lagged behind. Efforts to apply conventional radiolabeling methods to helminths have not always been successful. Experimental work with Schistosoma mansoni is reviewed to illustrate common problems encountered in surface labeling studies. These findings should provide insight for the future investigation of other helminth species.

A circular dichroism study of human erythrocyte ghost proteins during exposure to 2450 MHz microwave radiation

The effect of 2450 MHz microwave radiation on the proteins of human erythrocyte ghosts has been investigated using circular dichroism spectroscopy. A specially constructed waveguide inserted into the spectropolarimeter allowed the continuous recording of optical activity before, during and after microwave irradiation. The data indicate that high levels of microwave radiation (600 mW/g, specific absorption rate) induce decreases in alpha-helical conformation that may result from both thermal vibrations and increased strain on the intramolecular hydrogen bonds that maintain secondary structure. The latter effect may result from differential intramolecular interactions with the oscillating electric field. Spectrin (bands 1 and 2) isolated from the ghosts was more sensitive to microwave irradiation than intact ghosts, and spectrin-depleted vesicles were the least sensitive. The data, therefore, indicate that the alpha-helical conformation of spectrin is altered by high levels of microwave radiation.

Immunological evidence for the transmembrane nature of the rat liver receptor for asialoglycoproteins

Antibodies raised in goats against the rat hepatic receptor for desialylated glycoproteins were perfused through a rat liver and were specifically retained by the liver. These antireceptor antibodies also bound specifically to hepatocyte plasma membranes oriented with their cytoplasmic surface outward on polylysine-derivatized beads. These two phenomena were judged to be properties of distinct subpopulations of the antibody preparation because: (i) maximal adsorption of antibodies with membranes on polylysine beads did not affect subsequent retention by the perfused liver, and (ii) whereas perfusion resulted in a depletion of antibodies capable of blocking ligand binding, adsorption by the everted membrane preparation led to a relative enrichment of blocking antibodies. These results are interpreted as indicative of distinct antigenic determinants of the receptor being present on the two faces of the membrane and demonstrate a transbilayer disposition of the asialoglycoprotein receptor.

Immunoglobulins and complement in the skin of rhesus monkeys immunized with x-irradiated cercariae of Schistosoma japonicum

Skin sections of rhesus monkeys immunized with X-irradiated Schistosoma japonicum cercariae were stained by an unlabeled antibody enzyme method for the detection of IgG, IgM, IgA, IgE, and C3. While all of them could be found in the skin lesions, their distribution patterns varied with time and reactions. In whealing reaginic reactions, IgE appeared prominent, having an affinity to the mast cells. In Arthus-like reactions, IgG was predominant. IgG complexes were found on the schistosomula, on the walls of blood vessels, and in granulocytes near the schistosomula. In the late stage of Arthus-like reactions and in delayed hypersensitive reactions, IgA was predominant in granulocytes, mononuclear cells, and macrophages. Characteristics of each immunoglobulin pattern seemed to reflect its function in the effector mechanism. It may be speculated that these immunoglobulins and C3, together with effector cells, synergistically and sequentially destroy schistosomula in the skin.

Ganglioside headgroup dynamics

Gangliosides, spin-labelled specifically on N-acetylneuraminic acid residues or on random-headgroup sugars, have been used to extend previous studies of headgroup behaviour. Headgroup sugar mobility is seen to be homogeneous and relatively unrestricted in a range of systems including three lines of cultured cells. The effects of temperature and pH have been considered. Binding of small quantities of the lectin, wheat germ agglutinin, was found to increase average headgroup mobility for gangliosides in lipid bilayers, most likely as a result of a disordering effect on ganglioside clusters.

Effect of exogenous lipids and lipoproteins on the primary immune response in vitro

Cholesterol and certain lipoproteins have regulatory effects on the primary immune responses of murine spleen cells in vitro. The plaque-forming cell (PFC) responses to sheep red blood cells of trinitrophenylated Brucella abortus were studied in complete, lipid-depleted or lipoprotein-reconstituted media. The requirement for exogenous low density lipoprotein (LDL) and its cholesterol moiety was established by comparison of the yield of PFC in cell cultures deprived of lipoproteins with that in cultures to which specific classes of lipoproteins were added. The spleen cells in complete medium yielded about 10-fold greater PFC responses than cells in lipoprotein-deficient medium. In lipoprotein-deficient media, human LDL completely reversed the decreased immune response, LDL lipids and free cholesterol partially reversed the deficit, the human high density lipoproteins and an apo B phospholipid complex were ineffective. In complete media, cholesterol at higher concentrations (100--200 microgram/ml) and LDL lipids partially inhibited the primary immune response. Exogenous cholesterol was required for the in vitro response to both thymus-dependent and thymus-independent antigens.

Characterization and localization of a flagellar-specific membrane glycoprotein in Euglena

Purified flagella from Euglena yield a unique high molecular weight glycoprotein when treated with low concentrations of nonionic detergents. This glycoprotein termed "xyloglycorien" cannot be extracted from other regions of the cell, although a minor component that coextracts with xyloglycorien does have a counterpart in deflagellated cell bodies. Xyloglycorien is tentatively identified with a flagellar surface fuzzy layer that appears in negatively stained membrane vesicles of untreated flagella but not in similar vesicles after Nonidet P-40 extraction. The localization of xyloglycorien is further confirmed to be membrane associated by reciprocal extraction experiments using 12.5 mM lithium diiodosalicylate (LIS), which does not appreciably extract xyloglycorien, visibly solubilize membranes, or remove the fuzzy layer. Rabbit antibodies directed against the two major flagellar glycoproteins (xyloglycorien and mastigonemes) to some extent cross react, which may in part be caused by the large percentage of xylose found by thin-layer chromatography (TLC) analysis to be characteristic of both antigens. However, adsorption of anti-xyloglycorien sera with intact mastigonemes produced antibodies responding only to xyloglycorien, and vice versa, indicating the nonidentity of the two antigens. Antibodies or fragments of these antibodies used in immunofluorescence assays demonstrated that xyloglycorien is confined to the flagellum and possibly the adjacent reservoir and gullet. Binding could not be detected on the cell surface. The sum of these experiments suggests that, in addition to mastigonemes, at least one major membrane glycoprotein in Euglena is restricted to the flagellar domain and is not inserted into the contiguous cell surface region.

Desensitization of enucleated cells to hormones and role of cytoskeleton in control of normal hormonal response

Prostaglandin E1 and the beta-adrenergic hormone l-isoproterenol stimulated cyclic AMP formation in both nucleated and enucleated myeloid leukemic cells that could be induced to differentiate normally to mature cells by the macrophage- and granulocyte-inducing protein MGI (MGI+D+ cells). Enucleated as well as nucleated MGI+D+ cells also desensitized to these hormones, indicating that this desensitization is an extranuclear process. Nucleated or enucleated mutant myeloid leukemic cells that are not induced to differentiate (MGI-D- cells) were not desensitized to these hormones. The antitubulin alkaloids colchicine and vinblastine, but not the antimicrofilament compound cytochalasin B, increased the maximal hormone-induced formation of cyclic AMP in nucleated MGI+D+ cells but not in the MGI-D- cells. These alkaloids also inhibited the development of desensitization to l-isoproterenol and prostaglandin E1 in enucleated MGI+D+ cells. The results indicate that in MGI+D+ cells the cytoskeletal system puts constraints on the cells' ability to respond to these hormones and that these constraints are absent in the mutant MGI-D- cells. Because MGI+D+ but not MGI-D- cells can be induced to differentiate by the macrophage- and granulocyte-inducing protein, cytoskeletal constraints, which are also found in normal myeloid cells, may be necessary for cell competence to differentiate. The results support the suggestion that membrane cytoskeletal constraints generate may control the normal response and desensitization to membrane-mediated cell inducers.

Different species of messenger RNA encode receptor and secretory IgM mu chains differing at their carboxy termini

Biosynthetic studies in the presence of an inhibitor of glycosylation indicate that individual human lymphoma-derived cell lines can synthesize both membrne receptor and presumptive secretory forms of IgM mu chains. The receptor form has a larger polypeptide chain than the secretory form and possesses a different C-terminus, but similar N-terminus, consistent with the presence of a C-terminal hydrophobic "tail" for integral membrane binding. Messenger RNA isolated from these cells directs the synthesis of both forms of mu chains in a wheat germ translation system, indicating the presence of independent mRNAs for each form. It is proposed that the synthetic pathways for receptor and secretory IgM diverge at the post-transcriptional level, possibly by differential RNA splicing to give mRNA molecules with or without a translatable "tail" segment.

(Ca2+ + Mg2+)-ATPase in enriched sarcolemma from dog heart

An enriched fraction of plasma membranes was prepared from canine ventricle by a process which involved thorough disruption of membranes by vigorous homogenization in dilute suspension, sedimentation of contractile proteins and mitochondria at 3000 X g followed by sedimentation of a microsomal fraction at 200 000 X g. The microsomal suspension was then fractionated on a discontinuous sucrose gradient. Particles migrating in the density range 1.0591--1.1083 were characterized by (Na+ + K+)-ATPase activity and [3H]ouabain binding as being enriched in sarcolemma and were comprised of nonaggregated vesicles of diameter approx. 0.1 micron. These fractions contained (Ca2+ + Mg2+)-ATPase which appreared endogenous to the sarcolemma. The enzyme was solubilized using Triton X-100 and 1 M KCl and partially purified. Optimal Ca2+ concentration for enzyme activity was 5--10 microM. Both Na+ and K+ stimulated enzyme activity. It is suggested that the enzyme may be involved in the outward pumping of Ca2+ from the cardiac cell.

Overlapping functional systems: a theory for vertebrate central nervous system function in terms of informal systems analysis

An holistic theory of the functional organization of the central nervous system, a system at the level of the organ, in vertebrate organisms is presented as an alternative to localization of function by using two sets of complementary rules for systems designation derived from systems theory. These rules reveal three types of systems according to levels of operation and the origins of goals. These are: (1) the teleogenic or primary systems (reproductive, food-water intake-use, thermoregulative, immune, oxygen intake-use); (2) the teleozetic or subsystems (internal sensory and motor, external motor, external sensory); (3) the teleonomic systems or echelons (field, local circuit, basic functional unit, basic excitation unit). The systems, subsystems, and echelons are discussed with regard to their hierarchical relationships, the nature of their goals, and the supporting experimental evidence. The theory is discussed as an explicit statement of multileveled relationships for the analysis of the vertebrate CNS and, therefore, as presenting a paradigm for, or a way of thinking about, local and global brain theories, brain dysfunction, and brain evolution.

Characteristics of individual polymorphonuclear leucocyte motility obtained with a new opto-electronic method

An opto-electronic device has been used for a quantitative assessment of the motility of individual polymorphonuclear leucocytes (PMNL) adhering to a glass cover slip. One of the oculars in a phase contrast microscope is provided with a mini-array of 32 x 32 light-sensitive elements. These are connected to an electronic unit, capable of recording the number of light-intensity changes on each element and of visualizing the path of a cell on an oscilloscope screen, as a pattern of dots. The results clearly show that individual PMNL respond differently to environmental conditions; for instance, (i) raising the temperature increased the motility of cells to a maximum at around 39 degrees C and lowering the temperature from 42 degrees C restored their peak motility, (ii) protein was required at attachment depending on the temperature at attachment, (iii) endotoxin-activated normal human serum affected more drastically cells with a low initial motility and cytochalasin B more adversely influenced cells with a high initial motility, (iv) phagocytosis of yeast cells reduced the percentage of motile cells, which was more pronounced if the PMNL were washed before the motility measurement. The average motility of the PMNL was also diminished, although individual PMNL retained normal activity after ingestion of one or more yeast cells.

Recent advances in human cellular immunobiology

Several recent advances in human cellular immunology will have increasing impact on surgical science. First, lymphocytes are composed of diverse subpopulations with different biological properties. Second, lymphocytes and phagocytes expressed distinctive cell surface markers that reflect the specialized function of each cell. Third, different subpopulations of lymphocytes probably have one or only a few specific functions rather than being multipotential. Despite the seemingly complex heterogeneity of the immune system, the component parts collaborate in a highly integrated fashion. The recent elucidation of suppressor cells and their interaction with effector cells, for example, is a major conceptual advance. Fourth, the technology of immunologic science has advanced significantly. More discriminating methods for detecting lymphocyte markers and the ability to physically separate and analyze lymphocyte subpopulations will permit increasingly more refined insights into normal and abnormal immune responses. A number of important advances at the molecular level involving the disciplines of immunogenetics and immunochemistry have also been described but are beyond the scope of this review. Much work remains, however, in correlating these in vitro observations in the laboratory with in viro activity in the patient. It is now evident that the outcome of an immune response (or lack of it) represents a net balance of different components in the immunologic network that determine the time course, intensity of response, and the actual mechanisms of antigen elimination. A better understanding of these component parts of a normal immune response, and their deviations in disease states, is essential for designing more sophisticated therapeutic manipulations of the immune system. Attempts at "immune manipulation" aimed at stimulating or depleting the entire system are no more likely to be successful or reproducible than are attempts to "manipulate" the entire endocrine system. More meaningful results will occur when one can deal with individual components of an immune response (such as suppression or killing) and can precisely monitor the consequences of altering them.

B lymphocytes contain three species of mu chains

The murine B cell line cloned from a single cell, 38C-13, synthesizes three species of mu chains, that of cell surface membrane IgM (m-mu), that of secreted IgM (s-mu) and that of intracellular IgM (i-mu). They differ in their mobility on sodium dodecyl sulfate polyacrylamide gel electrophoresis. Sequence analysis of the different mu chains suggests that they are identical in the N-terminal as well as in their C-terminal positions. The ratio between incorporated radioactive monosaccharides to radioactive amino acids into the three different mu chains was higher in s-mu than in m-mu, but nevertheless m-mu migrated more slowly than s-mu on sodium dodecyl sulfate polyacrylamide gel electrophoresis. However, since this ratio may also be influenced by the rate of synthesis, it may not represent a real molar ratio of carbohydrate to protein. Studies with normal spleen cells clearly indicated the presence of the same three types of mu chains.

Presence of spectrin in untreated Friend erythroleukemic cells. Its accumulation upon treatment of the cells with dimethyl sulfoxide

Friend leukemia cells (FLC) are nucleated erythroid precursors, and are markedly stimulated towards more advanced stages of differentiation by treatment with dimethyl sulfoxide (DMSO). The presence of spectrin, an erythrocyte membrane protein, has been investigated in untreated and in DMSO-treated FLC by indirect immunofluorescence and by analysis in SDS-polyacrylamide gel electrophoresis of low-ionic-strength cell extracts immunoprecipitated with a monospecific anti-spectrin serum. Spectrin is detectable in significant amounts in the "inducible" clones prior to DMSO stimulation, and accumulates 4- to 5-fold upon addition of this compound to the cultures. Spectrin accumulation occurs rather early (24 hours after cell seeding) and reaches its peak on the third day to decline thereafter. Semiquantitative determinations of spectrin amounts present in DMSO-stimulated 745A and A degree 1 cells on the third day after treatment were 2.4 X 10(5) and 3.0 X 10(5) molecules/cell, respectively. Spectrin is also detectable in very low amounts in an "uninducible" line of FLC, and is not accumulated upon DMSO treatment thereof, whereas treatment with hemin does cause a significant increase of spectrin-positive cells. These data indicate that spectrin is a convenient "early" marker for in vitro studies of erythropoiesis.

The effects of asbestos on macrophages

The exact role of the alveolar macrophage in the pathogenesis of asbestosis is not known. Most studies of the effect of asbestos on macrophages have been concerned with the in vitro biochemical or cytotoxic properties of the dust and have made use of peritoneal macrophages. In general, chrysotile had a toxic effect on the macrophages, whereas amphibole varieties did not. Most forms of absetos, however, are actively fibrogenic in man and animals, and there is no clear correlation between in vitro cytotoxicity of various forms of asbestos and their fibrogenicity. Recent experiments in which animals are exposed to asbestos in vivo provide evidence of alteration of macrophage activity, as demonstrated by changes in surface morphology and IgG receptor sites, as well as released of various secretory products. Deposition of complement components found on the surface of alveolar marcophages from animals exposed to asbestos could be a manifestation of a humoral immune response directed against an altered cell. The capacity of macrophages to participate in inflammation, tissue repair, and immunity suggests an immunopathogenic concept for the development of asbestosis.

Subaxolemmal filamentous network in the giant nerve fiber of the squid (Loligo pealei L.) and its possible role in excitability

A new technique utilizing the squid giant nerve fiber has been developed which permits direct examination of the inner face of the axolemma by scanning electron microscopy. The axoplasm was removed sequentially in a 15-mm long segment of the fiber by intracellular perfusion with a solution of KF, KCl, Ca++-containing seawater, or with pronase. The action potential of the fibers was monitored during these treatments. After brief prefixation in 1% paraformaldehyde and 1% glutaraldehyde, the perfused segment was opened by a lne could be related to information on the detailed morphology of the cytoplasmic face of the axolemma and the ectoplasm. The results obtained by scanning electron microscopy were further substantiated by transmission electron microscopy of thin sections. In addition, living axons were studied with polarized light during axoplasm removal, and the identification of actin by heavy meromyosin labeling and sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis was accomplished. These observations demonstrate that a three-dimensional network of interwoven filaments, consisting partly of an actinlike protein, is firmly attached to the axolemma. The axoplasmic face of fibers in which the filaments have been removed partially after perfusion with pronase displays smooth membranous blebs and large profiles which sppose the axolemma. In fibers where the excitability has been suppressed by pronase perfusion, approximately one-third of the inner face of the axolemma in the perfusion zone is free of filaments. It is hypothesized that the attachment of axoplasm filaments to the axolemma may have a role in the maintenance of the normal morphology of the axolemma, and, thus, in some aspect of excitability.

Organization of extracellular proteins on the connective tissue cell surface: relevance to cell-matrix interactions in vitro and in vivo

A model has been developed that proposes a cell surface-associated protein meshwork, composed in part of fibronectin and collagen, for a connective tissue cell attached to a substratum. In support of this model are the observations that collagen and fibronectin interact and that these proteins are similarly distributed on the fibroblast cell surface. We suggest that this external meshwork interacts directly or indirectly with the internal cytoskeleton and with the extracellular matrix and thereby mediates several cellular properties, including adhesion, shape, and motility. Loss of cell surface fibronectin as a result of viral transformation, or due to treatment of normal cells with tunicamycin, an inhibitor of protein glycosylation, may contribute to the reduced adhesion and altered morphology observed in these circumstances. We therefore predict that the changes in these properties observed with virally transformed cells, mitotic cells, and cells treated with proteolytic enzymes are related to alterations in the external protein meshwork.

Photoelectron microscopy of cell surfaces

Photoelectron micrographs of fixed, unstained, uncoated chicken embryo fibroblasts and absolute photoelectron quantum yields in the 180-230 nm wavelength band of L-fucose, D-galactose, D-glucose, N-acetyl-D-glucosamine, and the sucrose polymer Ficoll are reported. The quantum yields of the saccharides are low compared to the reference dye, phthalocyanine, and fall in the same range as those previously measured for amino acids and membrane phospholipids. Photoelectron micrographs of the unstained and uncoated cells inhibit considerable surface detail. The photoelectron quantum yield data and the micrographs indicate that surface relief is the dominant source of contrast.

The structural transitions of erythrocyte membranes induced by cyclic AMP

The generalized structural transitions of erythrocyte membranes induced by cyclic AMP were registered by ESR, fluorescence, freeze-fracture and circular dichroism methods. Two transitions different in nature were revealed. One, which arises at 10-(11)--10-(10) M cyclic AMP, is cooperative and may be considered as a consequence of interaction of cyclic AMP with a receptor. It was calculated that a structural rearrangement in one erythrocyte ghost is induced by three cyclic AMP molecules. As a result of it the membranes are "loosened". The other transition arises at 10-(10)--10-(8) M cyclic AMP and depends on the activity of the protein kinase system. This transition was shown to be non-cooperative and due to phosphorylation of membranous proteins. During this rearrangement the membranes are "stiffened". Both transitions were demonstrated to relate to the membrane integrity.