Calcium-binding and its effect on circular dichroism of plant calmodulin

The Ca²⁺-binding properties of calmodulin purified from zucchini (Cucurbita pepo L.) has been determined. A value of 3.3 mol Ca²⁺ per mol of zucchini calmodulin was measured at pH 7.5 by equilibrium chromatography. The far-and near-UV circular-dichroic spectra of the Ca²⁺-and Mg²⁺-saturated as well as from the metal-free forms of zucchini calmodulin reveal that upon Ca²⁺-binding the -helix content increases. A comparison with the spectra of vertebrate calmodulin indicates that both calmodulin have a similar secondary structure, similar Ca²⁺-induced conformational changes and the same number of Ca²⁺-binding sites.Abbreviations CAPP 10-(3-aminopropyl)-2-chloro-phenothiazine - EGTA ethylene glycol-bis(-aminoethyl ether)-N,N,N,N-tetraacetic acid - EDTA ethylenediaminetetraacetic acid Dedicated to Prof. Dr. Karl Decker on the occasion of his 60th birthday     

Monoclonal antibodies against neoantigens of the terminal C5b-9 complex of human complement

Assembly of the terminal C5b-C9 complement components into the cytolytic C5b-9 complex is accompanied by exposure of characteristic neoantigens on the macromolecule. We report the production and characterization of mouse monoclonal antibodies to C9-dependent neoantigens of human C5b-9. Binding-inhibition assays with EDTA-human plasma and micro-ELISA assays with purified C9 showed that the antibodies did not react with native complement components and thus confirmed the specificity of the antibodies for the neoantigens. The monoclonal antibodies did, however, cross-react with cytolyticaIly inactive, fluid-phase C5b-9 complexes, Thus, expression of the neoantigenic determinants was not dependent on the formation of high molecular weight C9 polymers with the complex, since these are absent in fluid-phase C5b-9. Radioiodinated antibodies could be utilized in immunoradiometric assays for the detection and quantitation of C5b-9 on cell membranes. Cross-reactivities of the antibodies with C9-dependent neoantigens of several other animal species were examined and antibody clones cross-reacting with rabbit (clones 3BI, 3Dg, and 2F3), sheep (clones 3Dg and 2F3) and guinea-pig (clone 3D8) neoantigens were identified . Three of four tested clones (3D8, 2F3, IA12) precipitated C5b-9 complexes in double-diffusion assays, probably due to their interaction with multiple and repeating C9-epitopes on the terminal complexes. The monoclonal antibodies will be of value for definitive identification and quantitation of C5b-9 on cell membranes and in tissues, and for establishing immunoassays for detection and quantitation of terminal fluid-phase C5b-9 complexes in plasma.     

On the sexual reproduction ofDictyosiphon foeniculaceus (Phaeophyceae,Dictyosiphonales)

Dictyosiphon foeniculaceus from Sweden and Newfoundland was studied in laboratory culture. Zoids from unilocular sporangia developed into dioecious microscopic filamentous gametophytes which produced uniseriate plurilocular gametangia in low temperatures (0 to 8 °C). Zygotes and unfused isogametes gave rise to filamentous protonemata on which parenchymatous macroscopic sporophytes were formed. Isolates from Sweden and Newfoundland were interfertile. Although formed in culture, genetically unisexual sporophytes were not detected in nature. Female gametes ofD. foeniculaceus produced a sexual pheromone. It was identified as finavarrene, which is also known as the sperm attractant inAscophyllum nodosum.     

Pranceacanthus coccineus (Acanthaceae), a new genus and species from Amazonian brazil

The new genusPranceacanthus, apparently most closely related to the bitypic genusJuruasia, is described and illustrated. Its sole species,P. coccineus, has been collected on “terra firma” in lowland Amazonian Brazil in the states of Amazonas and Mato Grosso and in the territory of Rondônia.     

Electrorotation of lymphocytes—The influence of membrane events and nucleus

Electrorotation—the spin of cells in rotating high frequency electric fields—has been used to investigate properties of human peripheral blood lymphocytes. The rotation spectra of lymphocytes deviate from those of single shell spheres. The deviations are caused by the electrical properties of the nucleus in the cell interior.Electrorotation allows the distinction between successfully stimulated lymphocytes and unstimulated cells after application of concanavalin A. Notwithstanding the fact that only a proportion of the cells will be mitogenically stimulated we detected an enhanced cell membrane conductivity for the whole cell population immediately after the addition of mitogen.     

In vivo visualization of individual neurons in arthropod ganglia facilitates intracellular neuropil recording

Summary A simple method for the in vivo visualization of dye filled cells by laser illumination is used to characterize neurons in situ in the segmentai ganglia of the locust and the crayfish (Fig. 1). Neuron visualization provides the structural information necessary for identification of cells during an ongoing physiological experiment (Figs. 2, 3). Sequential penetrations of soma and neuropil as well as simultaneous double neuropil penetrations of spiking and nonspiking cells are facilitated by the visual control afforded by neuron visualization (Figs. 4, 5, 6). Furthermore, neuron visualization allows the sampling of cellular properties at multiple, predetermined sites in the dendritic and axonal arbors of identified neurons (Fig. 7) and aids in establishing synaptic connectivity through double neuropil recordings (Fig. 8).     

Cyclic AMP-induced reversible decrease in cAMP-binding to cell surface receptors of Dictyostelium discoideum

Abstract Adaptation may be the result of a change in affinity and/or number of cAMP-binding sites at the cell surface. To test this possibility we used agip 53, a mutant that does not synthesize cAMP in response to cAMP stimulation. cAMP induced a fast decrease in cAMP-binding to aggregation-competent cells, which reached a maximum at 10–20 s and was reversible with a t _0.5 of about 70 s. The decrease in cAMP-binding involved 46000 sites per cell and was mainly due to a reduction in the apparent affinity for cAMP-binding and to a smaller extent to slowly dissociating cAMP. Our results suggest that under these conditions only a fraction of the cAMP-binding sites at the cell surface are involved in transmembrane signalling, which is indeed observed for many of the physiological responses in Dictyostelium discoideum .     

The effect of calmodulin and far-red light on the kinetic properties of the mitochondrial and microsomal calcium-ion transport system from corn

The kinetic properties of active Ca²⁺ transport into mitochondria and microsomal membrane vesicles prepared from coleoptiles of dark-and light-grown corn seedlings have been studied. The apparent values for K _m and V _max for Ca²⁺ of the mitochondrial transport system from dark-grown plants are about one order of magnitude higher than those from the microsomal transport system. Calmodulin has no effect on the Ca²⁺ accumulation into mitochondria whereas the apparent maximum transport velocity and affinity for Ca²⁺ of the microsomal Ca²⁺-transport system are both increased by calmodulin. When intact corn seedlings are irradiated with far-red light, the calmodulin-induced increase of the apparent maximum transport velocity and affinity for Ca²⁺ can no longer be observed. From these data it can be concluded that the low cytoplasmic Ca²⁺ concentration in the cytoplasm of coleoptile cells from dark-grown corn is maintained by a calmodulin-regulated Ca²⁺ pump. Irradiation with photomorphogenically active far-red light lowers the Ca²⁺-transport activity and thus causes an increase of the cytoplasmic, free-Ca²⁺ concentration. The physiological implications will be discussed.