Mode of interaction of polyoxyethyleneglycol detergents with membrane proteins

Binding of dodecyloctaethyleneglycol monoether (C12E3) and purified Triton X-100 to various integral membrane proteins was studied by chromatographic procedures. Binding capacity decreased in the following order: bovine rhodopsin greater than photochemical reaction center greater than sarcoplasmic reticulum Ca2+-ATPase. The detergents were bound in different amounts to the proteins and less than corresponding to the aggregation number of the pure micelles. Appreciable binding of C12E8 to Ca2+-ATPase was observed far below the critical micelle concentration, consistent with interaction of the membrane protein with non-micellar detergent. Model calculations indicate that the detergents cannot combine with the membrane proteins, forming an oblate ring similar to that of pure detergent micelles, such as has been previously proposed for e.g. cytochrome b5 [Robinson and Tanford (1975) Biochemistry, 14, 365-378]. Other arrangements (prolate and monolayer rings), in which all detergent molecules are in contact with the protein, are considered as alternatives for covering the hydrophobic surface of the membrane protein with a continuous layer of detergent.     

Ion movement through gramicidin A channels. Studies on the diffusion-controlled association step

The permeability characteristics of gramicidin A channels are generally considered to reflect accurately the intrinsic properties of the channels themselves; i.e., the aqueous convergence regions are assumed to be negligible barriers for ion movement through the channels. The validity of this assumption has been examined by an analysis of gramicidin A single-channel current-voltage characteristics up to very high potentials (500 mV). At low permeant ion concentrations the currents approach a voltage-independent limiting value, whose magnitude is proportional to the permeant ion concentration. The magnitude of this current is decreased by experimental maneuvers that decrease the aqueous diffusion coefficient of the ions. It is concluded that the magnitude of this limiting current is determined by the diffusive ion movement through the aqueous convergence regions up to the channel entrance. It is further shown that the small-signal (ohmic) permeability properties also reflect the existence of the aqueous diffusion limitation. These results have considerable consequences for the construction of kinetic models for ion movement through gramicidin A channels. It is shown that the simple two-site-three-barrier model commonly used to interpret gramicidin A permeability data may lead to erroneous conclusions, as biionic potentials will be concentration dependent even when the channel is occupied by at most one ion. The aqueous diffusion limitation must be considered explicitly in the analysis of gramicidin A permeability characteristics. Some implications for understanding the properties of ion-conducting channels in biological membranes will be considered.     

DNA-dependent in vitro synthesis of enzymes of the galactose operon of Escherichia coli

Summary Two active enzymes of the galactose operon of Escherichia coli, uridyl transferase and galactokinase have been synthesized with high yields in a DNA dependent system for protein synthesis. The unspecific blank values amount to less than two percent of the rate obtained under optimal conditions and permit the accurate determination of even a small fraction of the maximum synthesis rate. Therefore this system provides a sensitive assay for the biological activity of DNA that contains the intact galactose operon of Escherichia coli.The synthesis of these galactose enzymes is to a high extent dependent on the presence of cyclic adenosine-3:5-monophosphate.D-fucose, known as an inducer of the galactose operon in vivo, stimulates the synthesis of galactokinase, indicating that the repressor of the galactose operon in active under these conditions. This stimulation is not observed, if the bacterial extract is prepared from a strain defective for the galactose repressor or if the DNA carries an operator constitutive mutation in the galactose operon. Therefore the stimulation by D-fucose is true derepression.     

Die Carotinoide der grünen Schwefelbakterien: Carotinoidzusammensetzung in 18 Stämmen

Summary The composition of the carotenoids in 18 strains of photosynthetic green sulfur bacteria has been investigated.Chlorobactene predominates in all strains; this pigment seems to be characteristic for all photosynthetic green sulfur bacteria. This main carotenoid is accompanied by various amounts of precursors and the hydroxy compounds of all appearing pigments.     

Über Fibrillärstrukturen im Nebennierenmark von Haus und Wildmeerschweinchen (Cavia aperea f. porcellus L. und Cavia aperea tschudii Fitzinger)

Zusammenfassung Im Nebennierenmark von adulten Wildmeerschweinchen (Cavia aperea tschudii) und Hausmeerschweinchen (Cavia aperea f. porcellus) werden bisher unbekannte intrazelluläre Fibrillenstrukturen nachgewiesen. Licht- und elektronenmikroskopische Befunde zeigen, daß in bestimmten Markzellen Filamentbündel in Gruppen auftreten, die durch das Perikaryon bis zur Zellperipherie zu verfolgen sind. Sie fasern in der Nähe des Plasmalemms auf und bilden desmosomenähnliche Kontaktflächen. Die Einzelfilamente sind ca. 70–100 Å dick. Beim Chinchilla konnten im Mark keine Filamentstränge festgestellt werden, beim Haus- und Wildmeerschweinchen kommen sie in unterschiedlicher Häufigkeit vor.

---

Intracellular fibrils in the adrenal medulla of domesticated and wild guinea pigs (Cavia aperea f. porcellus L. and Cavia aperea tschudii fitzinger)

Summary By light and electron microscopic observations intracellular fibrils were found in the adrenal medulla of adult wild (Cavia aperea tschudii) and domesticated guinea pigs (Cavia aperea f. porcellus). In certain cells of the adrenal medulla bundles of filaments can be traced from the perinuclear region into the periphery of the cells. Near the plasma membrane they split apart and attach to the desmosome-like regions. The individual filaments are about 70–100 Å in diameter. In adrenal medullary cells of chinchilla no fibrillar strands were observed, in wild and domesticated guinea pigs they occur in different numbers.

---

---

Die Untersuchung wurde mit dankenswerter Hilfe der Deutschen Forschungsgemeinschaft durchgeführt.     

Growth of Mycobacterium lepraemurium in Cultures of Mouse Peritoneal Macrophages

Successful growth of Mycobacterium lepraemurium was observed in cultures of mouse peritoneal macrophages. The optimal host cell maintenance medium was composed of 40% horse serum, 50% of the chemically defined medium NCTC 109, and 10% of a 1:5 dilution of beef embryo extract, supplemented with both liver extract and ferric nitrate. Multiplication of the bacilli was observed in 1 week and maximal growth in 6 to 7 weeks. All macrophages were filled with tens to hundreds of the organisms in cultures showing maximal growth. Glycerol caused an increase in the normal length of M. lepraemurium, without a corresponding increase in the number of the bacilli. Elongation of M. lepraemurium was observed 3 or 4 days after infection. Rapid and uniform growth of M. lepraemurium was achieved in serially transferred cultures (subcultures). The cumulative increase of the number of intracellular bacilli was 1.4 x 10(20)-fold in 14 transfers over a period of 68 weeks in one series, and 10(17)-fold in 12 transfers over a period of 56 weeks in another series. The generation time of M. lepraemurium was 7 days, a growth rate which approximates the fastest growth of the organisms in vivo. Organisms harvested from cultures at various stages of growth produced murine leprosy in mice, but showed no growth in bacteriological media. The present model offers an opportunity for studies on the host-parasite relationship without the complication of extracellular growth of the parasites.     

A Monitor for Airborne Bacteria

A unique agar drum sampler is described which indicates, continuously, the number of viable, bacterial particles per unit volume of air at the time and point of sampling. By selection of the timer and the sampling rate the sampler is suitable for quite a wide range of concentration and time. An impaction line of 484 in. greatly increases the capacity of this device over slit samplers and other instruments designed to give time-concentration data for viable airborne particles. This sampler should prove useful for: (i) monitoring airborne bacteria in hospitals, public places, and food and industrial plants; (ii) decay rate studies of bacterial aerosols; (iii) evaluation of aerial germicides; (iv) determination of effectiveness of air conditioning systems in removing airborne bacteria; and (v) many other studies in aerobiology.