N-2-acetylaminofluorene modification of poly(dG-m5dC)·poly(dG-m5dC) induces the Z-DNA conformation

Poly(dG-m⁵dC)·poly(dG-m⁵dC) was modified by treatment with N-acetoxy-N-2-acetylaminofluorene (N-Aco-AAF) and its conformation examined by circular dichroism (CD) and susceptibility to S₁ nuclease digestion. A sample with a modification level of 10% shows a CD spectrum characteristic of the Z form and is resistant to digestion by S₁ nuclease. The relative reactivity of several polymers with N-Aco-AAF was shown to follow the order of ease of formation of Z DNA: poly(dG-m⁵dC)·poly(dG-m⁵dC) > poly(dG-dC)·poly(dG-dC) > poly(dG)·poly(dC). This suggests that AAF reacts more readily with Z DNA than B DNA.     

Phase transition kinetics of phosphatidic acid bilayers A stopped-flow study of the electrostatically induced transition

The kinetics of the electrostatically induced phase transition of dimyristoyl phosphatidic acid bilayers was followed using the stopped-flow technique. The phase transition was triggered by a fast change in the pH or the magnesium ion concentration and followed by recording the time dependence of the absorbance. When the phase transition was induced by a pH jump the time course of the absorbance could be described by two exponentials, their time constants displaying the for cooperative processes characteristic maximum at the transition midpoint. The time constants are in the 10 and 100 ms range for the H⁺ triggered transition from the fluid to the ordered state. A third slower process shows no appreciable temperature dependence and is probably caused by vesicle aggregation. For the OH^--induced transition fron the ordered to the fluid state the time constants are in the 100 and 1000 ms range. The fluid-ordered transition could also be triggered by addition of magnesium ions. Of the several observed processes only the fastest in the 10–100 ms time range could definitely be assigned to the fluid-ordered transition while the others are due to aggregation phenomena. The experimental data were compared with results obtained from pressure jump experiments and could be interpreted on the basis of theories for non-equilibrium relaxation.     

Fluorimetric determination of carbamoyl phosphate

A simple fluorimetric assay for the determination of carbamoyl phosphate in tissue extracts is described. In the assay, production of ATP from carbamoyl phosphate and ADP by carbamate kinase is coupled to the formation of NADPH, using glucose, hexokinase, NADP⁺, and glucose-6-phosphate dehydrogenase. Production of NADPH in this system proved to be equal to the amount of carbamoyl phosphate present.     

Trace fossils from Lower Miocene (Ottnangian) molasse deposits of Upper Austria

Lower Miocene siliciclastic sediments of the Vöckla Schichten and Atzbacher Sande, Austria, contain a shallow-water trace-fossil assemblage of the Cruziana ichnofacies includingSkolithos isp.,Planolites ? beverleyensis, Ophiomorpha annulata, O.nodosa, Rosselia socialis, Cylindrichnus concentricus, Scolicia isp., andBichordites monastiriensis. The ichnogenusRosselia and the ichnospeciesRosselia socialis are revised. Analysis ofScolicia isp. andB. monastiriensis provides new information about their morphology and ichnotaxonomy.     

The ontogeny and distribution of B cells in normal and mutant immune-defective CBA/N mice: two-parameter analysis of surface IgM and IgD

A dual-laser fluorescence-activated cell sorter was utilized to study the distribution of the surface IgM and IgD on individual B cells of normal and immune-defective CBA/N mice. Cells from different lymphoid organs and from developing mice were studied. Two major populations of cells were seen. Those with low densities of surface IgM and intermediate-high densities of surface IgD were relatively or totally absent from the bone marrow, spleens, and lymph nodes of adult, immune-defective (CBA/N x DBA/2)F1 male mice, and developed late in ontogeny in the lymphoid organs of normal F1 female mice. By contrast, the second major population, with intermediate-high surface IgM and low surface IgD, was found in highest frequency in the lymphoid organs of immature mice, the bone marrow of adult mice, and the lymphoid organs of F1 male mice compared to F1 female mice at any age. These two major populations of B cells were further subdivided into five groups of cells to better define the surface IgM and IgD characteristics of developing B cells of immune-defective and normal mice. The relationship of these groups of cells to populations defined by other criteria are discussed.     

Destruction of Various Kinds of Mycobacteria in Milk by Pasteurization

Various strains of unclassified mycobacteria, Mycobacterium tuberculosis (including H37Rv strains), M. bovis, M. avium, M. fortuitum, and bacille Calmette-Guerin, were exposed to the temperature and time of pasteurization in skim milk in test tubes. Of the 195 strains tested, there were a few surviving colonies among 6 of 33 skotochromogens, 1 of 26 photochromogens, 10 of 79 nonchromogens, and 1 of 9 rapid growers. Subcultures of the surviving colonies failed to resist the pasteurization tests on subsequent trials.     

Properties of steroid sulphatase and arylsulphatase activities of human placenta

1. The properties of enzyme activities hydrolysing the sulphate esters of dehydroepiandrosterone, oestrone and p-nitrophenol are reported. The preparation studied was obtained from the microsomal fraction of human placenta by ultrasonic treatment and addition of Triton X-100. 2. The behaviour of the preparation during sedimentation at 105000g and attempts at purification indicated that the activities were particulate. Electron microscopy demonstrated the rupture of vesicular structures approx. 0.5mu in diameter concurrent with the release of activity. 3. The three activities were always associated throughout repeated attempts at separation by sucrose-density-gradient centrifugation and Sephadex-gel filtration. On the basis of kinetic studies, stability studies and treatment with butanol and ribonuclease it was concluded that a separate enzyme is responsible for each of the three activities. Widely varying plots of activity as a function of pH were consistent with this conclusion. 4. On the basis of sensitivity of the enzymes hydrolysing dehydroepiandrosterone sulphate and oestrone sulphate to ribonuclease and sensitivity of all three enzymes to lipase, it was concluded that the three enzymes are bound to a particle containing lipid and RNA. Enzymic activity is dependent on structural integrity of the particle. 5. A spectrophotometric method for the assay of oestrone sulphate hydrolysis is described. 6. Hydrolysis of nitrocatechol sulphate by human placenta under conditions described for arylsulphatases A and B is reported.