Antithrombin III binds to human platelets

The receptor site for antithrombin III (AT III) was investigated in normal human platelets. [¹²⁵I] iodinated AT III was utilized as tracer for the binding assay. Equilibrium of AT III binding was reached within 2 min. The binding capacity was pH-dependent with the optimum around pH 7.0. Binding specificity was demonstrated by inhibition of [¹²⁵I] AT III ligation using an excess amount of non-labeled AT III. The AT III·heparin complex did not supress [¹²⁵I] AT III binding. Analysis of binding data by Scatchard plot revealed a single class of binding sites with K_d of 3.2 × 10^?7 M and binding capacity of 3840 per platelet.     

Native and reconstituted chromosome fiber fragments

The structure of hen erythrocyte chromatin fibers was studied with the electron microscope. Chromatin fiber fragments with a length of about 5,000 Å and an average diameter of 320 Å are composed of 13 globular subunits (superbeads) which contain different numbers of nucleosomes. Their number average corresponds to 17 nucleosomes. — The interaction of lysine-rich histones with nucleosome chains was investigated by reconstitution experiments and was found to be semi-cooperative.     

Stereo high voltage electron microscopy of melanophores : Matrix transformations during pigment movements and the effects of cold and colchicine

Pigment migration in isolated melanophores of the angelfish, Pterophyllum scalare, has been studied by high voltage electron microscopy. Cells were isolated from the scales by collagenase and allowed to spread on Formvar and carbon-coated gold grids. Melanophores were then fixed by glutaraldehyde and osmium tetroxide and critical-point dried for viewing of whole cells in a high voltage electron microscope (1000 kV). The three-dimensional organization of the cytoplasmic matrix was stereoscopically examined in different states of pigment distribution, as well as under cold and colchicine treatment. The most prominent matrix constituent is an extensive mesh of cytoplasmic filaments (microtrabeculae) 2–18 nm in diameter that make contact to microtubules, pigment granules, and mitochondria. Microtrabeculae undergo dramatic changes in structural appearance in association with different phases of pigment movements. Cells fixed in the process of pigment aggregation are characterized by thickened and beaded trabeculae which may form irregular clots. Part of this material trails behind centripetally moving melanosomes. In dispersing cells, microtrabeculae are straight and of relatively uniform thickness throughout their length and form a highly ordered three-dimensional lattice. Reconstruction of the mesh in part precedes the arrival of pigment granules.Under the influence of cold or colchicine treatment, microtrabeculae show a high degree of polymorphism, being beaded, branched, or flattened with globose ends. Rather formless heaps are found associated with the surface of pigment granules. Since, however, these treatments also remove microtubules, the other important component of the cytoplasmic frame, alterations in microtrabecular structure may simply be mediated through removal of this organelle. In an attempt to separate the effects on microtrabeculae and microtubules from one another, cells have been cold-treated for only 15 min, a procedure that leaves a considerable portion of microtubules intact. Also under these conditions, microtrabeculae are beaded or transformed to globose heaps and flattened sheets.The observations suggest an involvement of microtrabeculae in the process of granule movement. Centripetal melanosome migration thereby seems associated with a collapse of microtrabeculae which again are reconstructed during pigment dispersion. The cold and colchicine experiments indicate direct effects of these agents on the structure and possibly also the function of the trabecular mesh. The significance and possible chemical composition of microtrabeculae is discussed.     

Electron microscopical-immunocytochemical evidence of ecdysteroids in the prothoracic gland of Galleria mellonella

Summary Fixation of prothoracic glands of Galleria mellonella with a solution containing saponin permits immunocytochemical staining of the entire gland. By this means ecdysteroids were demonstrated electron microscopically to be present in the hyaloplasm and microtubules.Supported by Sächsische Akademie der Wissenschaften zu Leipzig     

Ultrastructure of the Y-organ of Astacus astacus (L.) (Crustacea) in relation to the moult cycle

Summary The electron microscopical investigation of Y-organs of Astacus astacus revealed that during intermoult (stage C) the cytoplasm is poorly developed and that it increases at premoult (stage D). It then shows the typical signs of steroid production, namely agranular endoplasmic reticulum and mitochondria of the tubular type. Furthermore, a larger type of mitochondria with a regular pattern of internal structure is described.Supported by Sächsische Akademie der Wissenschaften zu LeipzigWe are grateful for technical assistance to Mrs. B. Cosack und Mrs. A. Schmidt     

E. coli membranes become permeable to ions following T7-virus-infection

Summary Infection of E. coli with the viruses T7 or T3 leads to a dramatic efflux of potassium ions. This ion efflux is caused by the virus particle since no concomitant protein synthesis is required. T7 mutants carrying deletions in the M-gene (Schweiger et al., 1975), however, yield virus particles disturbed in the ion release.     

The major growth current through lily pollen tubes enters as K+ and leaves as H+

Growing lily (Lilium longiflorum Thunb.) pollen always drive a current into their tubes and out of their grains. The only external ions needed for growth (and the growth current) are K⁺, H⁺, and Ca²⁺. Increases in K⁺ immediately stimulate the current; while decreases in K⁺ immediately inhibit it. Comparable changes in H⁺ have the opposite effect; while those in Ca²⁺ have very little effect. We infer that most of the steady growth current is carried in by a potassium leak and out by a proton pump; but other considerations indicate that a minor, but controlling, component of the inward current consists of calcium ions.     

GD (-) Aachen,a new variant of deficient glucose-6-phosphate dehydrogenase

Summary A deficient G-6PD variant was discovered in 4 males of one family from north-western Germany. Five generations of this family could be studied.The deficient G-6PD was a new variant, called Gd (-) Aachen. Its main characteristics are the following: severe enzyme deficiency in erythrocytes (3% of normal), contrasting with an almost normal activity in leukocytes; normal molecular specific activity (i.e., normal ratio enzyme activity/cross-reacting material); slow mobility in starch gel electrophoresis (92–94% of normal); increased Michaelis constant for glucose-6-phosphate (60–70 M) and NADP⁺ (20–25 M); decreased inhibition constant by NADPH with respect to NADP⁺ (7 M); increased inhibition by ATP; normal utilization of the substrate analogues; slightly biphasic pH curve; thermal instability, and normal activation energy of the enzymatic reaction.The relationships between the hematologic disorders (severe and frequent hemolytic crises) and the unfavorable kinetic modifications are discussed.with the technical assistance of Joelle Marie and Dominique CottreauDedicated to Prof. Dr. H. Schonenberg, Aachen, on his 60th birthday. The first results of this work were presented in part at the Kongress der Deutschen Kinderärzte, München.     

Die Bedeutung der Elytren bei Vertretern desMelolontha-Flugtyps (Coleoptera)

The function of the flapping elytra was investigated in garden shafers (Melolontha melolontha L.) and rhinoceros beetles (Oryctes boas Fabr.).