Search

The conformational behavior of chlorocyclohexane (ClCH) adsorbed inside several representative zeolites such as completely siliceous ZSM-5, Na−Y, and siliceous Y (Si−Y) has been investigated by FT-Raman spectroscopy. The results have clearly shown that the conformational and dynamic properties of ClCH depend on the zeolitic framework structure, the presence of charge-balancing cations, as well as the Si/Al ratio. Compared to pure liquid, the population of equatorial conformation increases upon adsorption into ZSM-5. Apparently, the ZSM-5 framework stabilizes the equatorial conformation (with a larger molecular volume) via maximizing the van der Waals interactions between the host and guest. Within the ZSM-5 framework, the axial and equatorial conformers are still in dynamic equilibrium. It continues to shift toward the equatorial configuration upon lowering the temperature, and at 153 K the ClCH in ZSM-5 adopts the equatorial conformation exclusively. For the ClCH/Na−Y system, the situation is remarkably ...

We have examined the conformational properties of trans-1,4-dichlorocyclohexane (DCC) adsorbed in several zeolites, including completely siliceous ZSM-5, Na−Y and siliceous Y, by using FT-Raman spectroscopy. The results indicate that the conformational behavior of DCC is dependent on the zeolite framework structure, Si/Al ratio, and the charge-balancing cations. The conformational behavior of DCC in ZSM-5 differs from that in nonpolar solvents such as carbon tetrachloride in that the population of diequatorial (ee) conformer is significantly increased relative to the diaxial (aa) form upon adsorption. The ee and aa conformers are still in dynamic equilibrium as in solution, and lowering the temperature shifts the equilibrium further toward the ee configuration. The situation for DCC incorporated inside Na−Y is markedly different. Upon adsorption, the conformation of DCC is frozen by interactions with the extraframework sodium ions in the supercages of Na−Y. These interactions also lock the guest molecules...

Most of the applications of zeolites involve incorporating guest species into the framework. It is important to obtain structural knowledge of these sorbate/sorbent complexes. In this work, we outline the applications of FT-Raman spectroscopy in several areas of host–guest interactions in zeolitic systems such as detecting sorbate-induced phase transitions, investigating the conformational properties of guest species, probing the location of the guest molecules inside the zeolite and examining the cation–sorbate interactions.

The dynamic and conformational behavior of three related alkylcyclohexane molecules, cyclohexane (CH), methylcyclohexane (MCH), and trans-1,4-dimethylcyclohexane (DMCH), loaded within completely siliceous zeolite ZSM-5 has been investigated by variable temperature FT-Raman spectroscopy. Our results indicate that at room temperature CH molecules inside the ZSM-5 framework undergo significant reorientational motions around different axes as well as ring inversion and that the reorientational motions have ceased when the temperature is lowered to 153 K. For MCH and DMCH, in contrast, the major molecular motions are removed upon initial loading into the ZSM-5 framework. At low temperatures, the symmetry of CH inside ZSM-5 clearly deviates from the perfect D3d symmetry of the free molecule. At room temperature, the conformational equilibrium of MCH guest molecules still exists in the ZSM-5 host, but at low temperatures, MCH adopts the equatorial conformation exclusively. Interestingly, for DMCH absorption into...

The survival of Plasmodium falciparum-infected erythrocytes is enhanced by the sequestration of mature trophozoites and schizonts from the peripheral circulation. Cytoadherence of infected erythrocytes in vivo is associated with the presence of knobs on the erythrocyte surface, but we and others have shown recently that cytoadherence to C32 melanoma cells may occur in vitro in the absence of knobs. We show here that a knobless clone of P. falciparum adheres to the leukocyte differentiation antigen, CD36, suggesting that binding to CD36 is independent of the presence of knobs on the surface of the infected erythrocyte. This clone showed little cytoadherence to immobilized thrombospondin or to endothelial cells expressing the intercellular adhesion molecule 1. Furthermore, an Mr approximately 300-kD trypsin-sensitive protein doublet was immunoprecipitated from knobless trophozoite-infected erythrocytes. Finding a P. falciparum erythrocyte membrane protein 1 (PfEMP1)-like molecule on these infected erythrocytes is consistent with a role for PfEMP1 in cytoadherence to CD36 and C32 melanoma cells.

Erythrocytes infected with Plasmodium falciparum trophozoites and schizonts are not seen in the peripheral circulation because they attach to venular endothelium via knoblike structures on the infected erythrocyte membrane. We have recently shown that erythrocytes containing P. falciparum trophozoites and schizonts likewise attach to cultured human venous endothelial cells via knobs. In search of a more practical target cell for large scale binding studies designed to characterize and isolate the knob ligand, we tested various normal cells and continuous cell lines for their ability to bind P. falciparum-infected erythrocytes. Of the 18 cell types tested, binding of infected erythrocytes was observed to a human amelanotic melanoma cell line and amnion epithelial cells as well as to human aortic and umbilical vein endothelial cells. 96-100% of amelanotic melanoma cells bound 17±4 (±1 SEM) infected erythrocytes per positive cell, whereas fewer endothelial cells (4-59%) and amnion epithelial cells (8-19%) were capable of binding 12±5 and 4±1 infected erythrocytes per positive cell, respectively. Further studies designed to compare the mechanism of binding to the amelanotic melanoma cell line and endothelial cells showed the following results. First, that adhesion of infected erythrocytes to these two cell types was parasite stage-specific in that only erythrocytes containing late ring forms, trophozoites, and schizonts bound. Erythrocytes containing early ring forms, which do not attach to venular endothelium in vivo, did not bind to either cell type. Second, erythrocytes infected with trophozoites and schizonts of P. vivax or a knobless strain of P. falciparum, both of which continue to circulate in vivo, did not bind to either target cell type. Third, transmission electron microscopy showed that infected erythrocytes attached to the amelanotic melanoma cells via knobs. We conclude that cultured human endothelial cells and an amelanotic melanoma cell line share common determinants on their surface and that the mechanism of binding to these two different cell types is similar. The amelanotic melanoma cell line offers a useful substitute for endothelial cells in binding studies requiring large numbers of target cells.

Erythrocytes infected with Plasmodium falciparum develop knob-like protrusions on their membranes. Knobby (K+) parasites of the FCR-3 (Gambian) strain have been shown to possess a histidine-labelled protein of apparent molecular weight 80 000 which is absent from knobless (K−) variants of the same strain. Here we report similiar findings with K+ and K− parasites of another strain, the Malayan Camp strain, and also with cloned K+ and K− parasites of the FCR-3 strain. A histidine-labelled protein unique to the two K+ parasites was identified as a broad band with an apparent molecular weight of 89 000 on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The presence of this protein in both K+ Malayan Camp parasites and K+ FCR-3 (Gambian) parasites and its absence from K− parasites of both strains is consistent with this protein being a major component of knobs.

Human erythrocytes infected with five strains of Plasmodium falciparum and Aotus erythrocytes infected with three strains of P. falciparum were studied by thin-section and freeze-fracture electron microscopy. All strains of P. falciparum we studied induced electron-dense conical knobs, measuring 30-40 nm in height and 90-100 nm in diameter on erythrocyte membranes. Freeze-fracture demonstrated that the knobs were distributed over the membrane of both human and Aotus erythrocytes. A distinct difference was seen between the intramembrane particle (IMP) distribution over the knobs of human and Aotus erythrocyte membranes. There was no change in IMP distribution in infected human erythrocyte membranes, but infected Aotus erythrocytes showed an aggregation of IMP over the P face of the knobs with a clear zone at the base. This difference in IMP distribution was related only to the host species and not to parasite strains. Biochemical analysis demonstrated that a higher proportion of band 3 was bound to the cytoskeleton of uninfected Aotus erythrocytes than uninfected human erythrocytes after Triton X-100 extraction. This may account for the different effects of P. falciparum infection on IMP distribution in the two different cell types.

In a continuing study of patients with lymphoproliferative diseases, six adult patients were encountered with a distinctive malignant lymphoma of peripheral T-lymphocyte origin. Cell suspensions from lymph nodes of these patients contained a pleomorphic, cytologically atypical population of lymphocytes, of which an average 58% marked as T cells in the E-rosette test. The average percent of surface immunoglobulin-bearing B cells in these suspensions was 6%; they were of polyclonal distribution. Lymph node biopsies revealed a malignant lymphoma with certain characteristic features of the organization of the infiltrate, the morphology of the lymphoid cells, and the nature of non-lymphoid cellular elements. The average age of the patients was 67 years; they presented with generalized lymphadenopathy, anorexia, and significant loss of weight. Four patients hd lung and/or pleural involvement by lymphoma at presentation. The immunologic, pathologic, and clinical features of these patients serve to characterize this recently recognized malignant lymphoma further.

The subcellular location of the major malarial glycoprotein in erythrocytes infected with schizonts of Plasmodium falciparum has been studied by two methods. In the first, glycoproteins were labelled with [3H]glucosamine or [3H]isoleucine during in vitro culture. Trypsin treatment of intact infected erythrocytes caused no major qualitative or quantitative changes in [3H]glucosamine labelled glycoproteins or [3H]isoleucine labelled proteins separated by sodium dodecylsulfate polyacrylamide gel electrophoresis. However, in the presence of Triton X-100 the labelled glycoproteins and proteins were completely cleaved by trypsin. In the second method, two monoclonal antibodies which specifically immunoprecipitate the major 195 kDa glycoprotein failed to react on indirect immunofluoresence with intact non-fixed schizont-infected erythrocytes, but reacted strongly with saponin released schizonts indicating specificity for the surface of mature intracellular parasites. Immunoelectronmicroscopy using ferritin-conjugated secondary antibody confirmed the location of the epitope(s) recognized by these monoclonals on the surface of intracellular parasites. Ferritin particles were not associated with knob-bearing erythrocyte membranes. The results indicate that only a small proportion or none of the 195 kDa glycoprotein is on the surface of the infected erythrocyte and that the largest proportion is expressed on the surface of mature intraerythrocytic parasites.

Invasion of erythrocytes by malaria merozoites requires the formation of a junction of attachment between erythrocyte and merozoite membranes. The attachment junction initially forms at the apical region of the merozoite. It then moves around to the posterior of the merozoite as invasion proceeds. A monoclonal antibody against a 60-kDa merozoite protein (termed MCP-1 for merozoite capping protein 1) of Plasmodium falciparum reacts in an immunofluorescence pattern resembling the moving junction. By two-color immunofluorescence, MCP-1 was located at the attachment site formed between the merozoite apical region and erythrocyte. During invasion, MCP-1 separated and migrated around merozoites at the orifice of the parasitophorous vacuole. In newly-invaded erythrocytes, MCP-1 persisted at the pole of the young parasite nearest the erythrocyte membrane, suggesting its anterior-to-posterior movement. MCP-1 exhibited no variability in molecular mass among the FCR-3, Camp and 7G8 strains of P. falciparum, and the epitope was invariant in the P. falciparum strains studied. We conclude that MCP-1 may participate in merozoite invasion of erythrocytes by facilitating attachment or movement of the junction along the parasite cytoskeletal network.

Modification of the Golgi apparatus has been studied in rootcap cells through progressive states of normal cellular development. Large vesicles, with contents of considerable electron density, are produced by the hypertrophied portions of the Golgi cisternae of outer rootcap cells. These undergo change as they pass from the apparent site of their origin to and through the plasma membrane. This passage does not seem to involve discontinuities in the plasma membrane and it is assumed that the membranes of the Golgi-produced vesicles are incorporated into the plasma membrane. There is close packing of these bodies between the surface of the protoplast and the surface of the definable cell wall, with accompanying displacement of the protoplast around the masses. The discrete nature of the bodies is finally lost but their position is still discernible. Ultimately there is a disappearance of these masses, an increase in cell wall volume, and a return to smooth contour by the protoplast surface, paralleled by a return of the Golgi apparatus to an unhypertrophied state.

Responses of cellular organelles to purposely-induced mechanical injury, at or near the surfaces produced by excision of sections from maize root tips, have been studied. These responses are apparent in sections fixed within a few seconds of excision, hence they are essentially immediate. The pores in the nuclear envelope are enlarged and, frequently, proliferation of the nuclear envelope is apparent. The nuclear ground substance appears more granular; the nucleolus appears unchanged. Structural modifications are seen in the mitochondria, endoplasmic reticulum, and the plasma membrane, but there are no striking changes in the Golgi apparatus or the ground substance of the cytoplasm. Certain types of associations, not ordinarily seen in uninjured cells, between some cellular organelles, particularly mitochondria with mitochondria, mitochondria with proplastids, and both of these organelles with “lipid” bodies, are also injury responses.

In maize root meristem cells, fixed in KMnO4, embedded in epoxy resin, ultrathin sectioned, and studied with an electron microscope, the nuclear envelope is demonstrated to be a double membrane structure. In the nuclear envelope there are: pores of the sort reported in many species of animals and plants; different types of openings associated with extensions of both nuclear membranes into the cytoplasm; and also, often, large discontinuities. The nuclear envelope is a component of the general vesicular reticulum. The reticula of neighboring cells including the nuclear envelopes make up, at certain stages at least, a "systemic" structure. The status of the nuclear envelope as a component of the general cellular reticulum is recognized to change during differentiation. The existence of several types of discontinuities in the nuclear envelope and the extent of nuclear-cytoplasmic surface relationships indicated suggests alteration in concepts of transport and exchanges between nucleus and cytoplasm.

Plasmodium fragile infection of the toque monkey is a natural host-parasite association in which parasite sequestration occurs as during P. falciparum infection of humans. We have studied parasite sequestration of P. fragile and demonstrated the existence of a new property of cytoadherence of infected erythrocytes, "rosetting," which is defined as the agglutination of uninfected erythrocytes around parasitized erythrocytes. Rosetting in vitro and sequestration in vivo appear simultaneously as the parasite matures. The spleen plays a role in modulating cytoadherence; both sequestration and rosetting, which occur with cloned parasites from spleen-intact animals, are markedly reduced in splenectomized animals infected with parasites derived from the same clone. Sequestration and rosetting can be reversed by immune serum. Protease treatment of infected blood abolishes rosetting; however, if treatment is performed at an early stage of schizogony, rosetting reappears if parasites are allowed to further develop in the absence of protease. These results indicate that with P. fragile in its natural primate host, rosetting and sequestration are related to the presence on the infected erythrocyte surface of a parasite-derived antigenic component, the expression of which is modulated by the spleen.

The human malaria parasite Plasmodium falciparum synthesizes several proteins that are unusually rich in histidine. We therefore screened histidine analogues for their capacity to inhibit in vitro parasite growth. Analogues were added to cultures of ring-stage parasites, and parasite morphological development was assessed by light microscopy after a 22-hr culture. Inhibition of morphological development was identified as the appearance of condensed or pycnotic parasites rather than mature trophozoites. Inhibition of parasite protein synthesis was assessed by radioactivity counting of [ 3 H] isoleucine incorporated into acid-insoluble products and by sodium dodecyl sulfate polyacrylamide gel electrophoresis and fluorography of [ 3 H]histidine-labeled malarial proteins. 2-F- l -Histidine and 2-I- d , L-histidine exerted the most pronounced inhibitory effects, the fluoro-analogue being the more effective of the two. At a 0.125 mM concentration, both compounds inhibited parasite growth and 2-F- l -histidine also inhibited protein synthesis. At a 1.0 mM concentration, 2-azido- l -histidine, α-methyl- l -histidine and WR 177589A also inhibited P. falciparum growth and protein synthesis. Twenty other histidine analogues, including 5-F- l -histidine and 5-I- l -histidine, showed little or no effect under these conditions. The inhibitory histidine analogues may be of interest for antimalarial chemotherapy it they should prove to have greater effect on P. falciparum protein synthesis than on host protein synthesis.