No abstract

No abstract

The interaction of L-aromatic aminoacids with bases and nucleosides is described. Of these, L-tryptophan interacts more strongly with bases and nucleosides as indicated by nuclear magnetic resonance, circular dichroism and solubility measurements.A possible ring-ring type interaction between the aminoacid and bases or nucleosides is proposed; this interaction being such that the hydrodinamic behaviour of the DNA molecule is unchanged.Ultra violet irradiated DNA is protected by L-tryptophan. A mechanism of energy transfer from the DNA to tryptophan trough triplet-triplet states is discussed.In previous communications 2 we described the interaction of L-tryptophan with ribonucleosides and DNA, as studied by NMR and ultraviolet spectroscopy.In this paper, the interaction of L-tryptophan with ribonucleosides and DNA as shown by solubility, circular dichroism and viscosity measurements are reported. Also some preliminary results of the interaction of this aminoacid with DNA at excited levels, are included. Materials and MethodsNitrogen bases, DNA (salmon sperm) were obtained from Calbiochem and nucleosides from Sigma.For the solubility experiments, saturated solutions of bases or nucleosides at 60° were prepared. These solutions, and those containing besides the aminoacid were incubated at 30 °C in a shaking water bath. The incubation flaks had two compartments separated by a sintered glass disk. The sample was placed in one of those compartments. After four days of incubation the flasks were inverted and filtered through the disk in the bath, avoiding temperature changes. These experiments were run in triplicate; the standard deviation of the mean value of solubility being less than 6 percent.The circular dichroism measurements were performed on a Shimatzu Seisakusho QU50 instrument with a DC attachment model CD1. For the ultraviolet spectroscopy, a Beckman DU instrument was used.Viscosity determinations were performed with a Beckman rotatory viscosimeter. Nuclear Magnetic Resonance measurementsAll of the proton spectra were recorded on a Hitachi temperature of 30 °C. The chemical shifts were measured with respect to DSS as an internal standard and were calibrated by the usual side band modulation technique to within ± 0.3 cps. The samples were dissolved in D20 (99.7%) and acidified to pD2 with concentrated HCl. The pD of the solutions were checked before and after recording the spectra. Ultraviolet irradiation was done at room temperature with a General Electric 30 Watt-lamp (G30T8) at a distance of 25 cm from the surface of the solutions. The energy out put of the lamp was approximatively 90 ergs/sec mm 2 *. ResultsAs we have shown previously the interaction at pH 2 of L-tryptophan with ribonucleosides, was evaluated through the magnetic up-field shifts of the ribonucleosides protons as a function of tryptophan concentration.By using NMR techniques we also investigated other possible interactions between L-aminoacids and ribonucleosides.Of those which could be studied (i. e. those which had enough solubility in wa...

SummaryA method for large reduction of nucleic acid content of Saccharomyces cerevisae is described. This method is based on yeast suspension in phosphate solution (50mM), heat shock following the Maul et al. (Nature 228, 181 (1970)) procedure, and dialysis or washing with phosphate solution of alkaline pH. When the extraction process is carried out a t p H 12, sodium phosphate can be replaced by sodium chloride with the same results. Under these conditions the protein mg/nucleic acid mg ratio attains values of 50-60, (10 times the initial ratio). At this alkaline pH, washing can be done with distilled water with equally good results.

No abstract