Investigation of huge negative circular dichroism spectra of some nucleoproteins

Under certain conditions of preparation, DNA, whether free or complexed with polylysine or histone KAP (I, fl), produce huge negative circular dichroism (CD) spectra with maxima at about 270nm. In order to investigate the cause of these spectra, reconstituted polylysine-DNA complex was used as a model system. It was found that the CD change of DNA in the complex is not a linear function of the fraction of base pairs bound. Such a CD spectrum is not changed despite dilution up to 128 folds for as long as 12 hours. Difference CD spectra taken between free DNA and any of the complexes are qualitatively the same, and are similar to those of free DNA and nucleohistone KAP (Fasman et al., Biochemistry 9, 2814-2822, 1970), free DNA and direct mixed polylysine-DNA complexes, or free DNA in high salt (Chang et al., Biochemistry12, 3028-3032, 1973). The suggestion is made that this CD spectrum might be caused by specific conformational changes in DNA, perhaps belonging to the family of B to C transitions followed by a further structural distortion of DNA due to aggregation of the nucleoprotein molecules.     

Copper levels in cervical mucus during normal menstrual cycles

To establish the pattern of copper levels in cervical mucous, individual samples were taken from 10 normal women (aged 23-46), 2-3 times per week during the cycle. Analysis using a modification of the Stoner and Dasler wet ash microtechnique showed the lowest amounts of copper per 100 mg of dried ash (mean-3.2 mcg) in the ovulatory phase. The highest amount of copper was found in the secretory phase (mean 19.4 mcg). The copper level seemed to vary directly with the level of endogenous progesterone and inversely with the level of endogenous estrogen. No significant correlation between age and amount of copper secreted could be established because of the small size of the study.     

Cation Transport in Escherichia coli : VII. Potassium requirement for phosphate uptake

When Escherichia coli K-12 is grown in media containing limiting amounts of K, growth continues normally until all the extracellular K has been consumed. Thereafter the rates of growth, glucose consumption, and oxygen consumption decrease progressively, and the cell contents of K and P fall. These changes, referred to as K limitation, are all reversed by the addition of K. By specifically altering the ionic composition of the cells it was shown that these metabolic disturbances are not due to changes in the cell content of K or Na, but are directly related to the absence of K from the extracellular medium. The cell pool of inorganic P and the uptake of PO₄ from the medium are low in K-limited cells and are immediately stimulated by the addition of K, suggesting that the primary effect of K limitation is to inhibit PO₄ uptake. All the metabolic effects of K limitation can be attributed to inhibition of PO₄ uptake. The requirement of extracellular K for PO₄ uptake may be due to a coupling between the uptake of K and PO₄.     

Sodium absorption by barley roots: role of the dual mechanisms of alkali cation transport

Radioactively labeled Na(+) absorbed by barley roots was sequestered in an intracellular compartment or compartments ("inner" spaces) in which it was only very slowly exchangeable with exogenous Na(+). Absorption of this fraction proceeded at a constant rate for at least 1 hour.When the rate of Na(+) absorption was examined over the range of concentrations, 0.005 to 50 mm, the isotherm depicting the relation showed dual kinetics as follows. Over the range, 0.005 to 0.2 mm, a single Michaelis-Menten term describes the relation between the concentration of Na(+) and the rate of its absorption. The mechanism of Na(+) absorption operating over this range of concentrations, mechanism 1 of alkali cation transport, is severely inhibited in the presence of Ca(2+) and virtually rendered inoperative for Na(+) transport by the combined presence of Ca(2+) and K(+). The mechanism is equally effective in Na(+) transport whether Cl(-) or F(-) is the anion, but is somewhat inhibited when the anion is SO(4) (2-).Over the high range of concentrations, 0.5 to 50 mm Na(+), a second, low-affinity mechanism of Na(+) absorption comes into play. In the presence of Ca(2+) and K(+), this mechanism 2 is the only one to transport Na(+) effectively, since Na(+) absorption via mechanism 1 is virtually abolished under these conditions.Anaerobic conditions, low temperature, and the uncoupler, 2,4-dinitrophenol, inhibit Na(+) absorption both at low and high Na(+) concentrations.     

Identification of Indole-3-Acetic Acid in the Basidiomycete Schizophyllum commune

Indole-3-acetic acid (IAA) was detected in the ether extracts of culture filtrates of indigotin-producing strains of the basidiomycete Schizophyllum commune. Several solvents, known to give distinctly different R_F values for IAA, and 3 location reagents gave identical results with synthetic IAA and IAA found in the extract. Confirmation was obtained by the Avena straight growth test, split pea test, and ultraviolet absorption spectrum.     

Evaluation of Slit Sampler in Quantitative Studies of Bacterial Aerosols

Quantitative studies were conducted to evaluate the efficiency of the slit sampler in collecting airborne Serratia marcescens and Bacillus subtilis var. niger, and to compare it with the collecting efficiency of the all-glass impinger AGI-30. The slit sampler was approximately 50% less efficient than the AGI-30. This ratio remained the same whether liquid or dry cultures were disseminated when the sample was taken at 2 min of aerosol cloud life. At 30 min of aerosol cloud life, this ratio was approximately 30% for B. subtilis var. niger. S. marcescens recoveries by the slit sampler were, however, only 17% lower than the AGI-30 at 30 min of cloud age, indicating a possible interaction involving the more labile vegetative cells, aerosol age, and method of collection.     

Effects of Environmental Factors on the Survival of Airborne T-3 Coliphage

Experiments were conducted to determine the effects of storage temperatures, relative humidity, and additives on the survival of aerosolized Escherichia coli phage T-3. The aerosol stability of the coliphage, calculated as per cent recovery, was not affected by storage at 10 or -70 C for up to 4 months. However, an increase in aerosol decay rate of coliphage stored at 10 C was observed. The effect of humidities ranging from 20 to 90% relative humidity was studied, and it was observed that humidities lower than 70% relative humidity significantly reduce the survival of airborne coliphage. The effect of various compounds on the aerosol decay rate of T-3 coliphage was studied at 50 and 85% relative humidity. Addition of dextrose in 0.1 M concentrations to the disseminating fluid significantly reduced aerosol decay rate at 50% relative humidity without affecting the decay at 85%. Addition of spermine, spermidine-phosphate, thiourea, galacturonic acid, and glucosaminic acid, individually or in combination, had no effect on aerosol decay rates. The use of deuterium oxide as the suspending fluid for dissemination had no effect on aerosol stability of the coliphage.