Use Of 32P Research Articles

The Use of 32P Labelled Orthophosphate for the Assay of Chemotherapeutic Agents on Tumours Maintained in Organ Culture

The Use of 32 P Labelled Orthophosphate for the Assay of Chemotherapeutic Agents on Tumours Maintained in Organ Culture

A radiotracer study of the composition and properties of anodic oxide films on tantalum and niobium

The composition of anodic oxide films formed on tantalum in phosphoric and sulphuric acids and on niobium in phosphoric acid has been determined by the use of 32P- and 35S-labelled electrolytes. The films consist in all cases of a layer of stoichiometric pentoxide next to the metal and an outer layer characteristic of the anodizing electrolyte. This layered structure can only arise through the movement of both cations and anions during the growth of the film. The amount of a particular species that is incorporated into the film from the electrolyte increases with increasing solution concentration and current density and decreases with increasing temperature; variations in the amount of included material with temperature are entirely accounted for by changes in the relative contributions of cation and anion movement during film growth.It is shown that differences between films formed in phosphoric and sulphuric acids are due to the much larger degree of incorporation that occurs with the former. The incorporation of phosphorus into the oxide results in a decrease of dielectric constant and an increase of dielectric strength.

Accumulation of inorganic polyphosphate in mutants of Neurospora crassa

1. 1. 53 strains of Neurospora crassa, representing 4 wild types and 40 mutant loci, were examined for accumulation of acid-soluble inorganic polyphosphate. When grown on a limited supply of growth factor, most of the mutants were found to accumulate polyphosphate, though the amounts varied widely. 2. 2. The time sequence of polyphosphate accumulation was studied in shaken cultures of the histidine-requiring strain, C-84. When growth ceased due to exhaustion of the amino acid, the RNA content of the mycelium dropped sharply. Concomitantly, acid-soluble polyphosphate accumulated; the levels of other phosphorus compounds, including the acid-insoluble polyphosphate, were not affected. 3. 3. By the use of 32P it was demonstrated that, in C-84, extensive degradation of RNA occurred upon exhaustion of the histidine. The phosphorus released from RNA was converted to polyphosphate and constituted a major source of phosphorus for polyphosphate accumulation. Similar observations were made with other mutant strains, though the details of the pattern of growth, RNA degradation and polyphosphate accumulation varied from strain to strain. 4. 4. Inhibition of the growth of Neurospora strains by withholding a macronutrient or by addition of a metabolic inhibitor did not, in general, induce either RNA degradation or polyphosphate accumulation. However, when mycelium was transferred to medium lacking the carbon source, sucrose, extensive degradation of RNA took place. Acid-soluble polyphosphate and inorganic orthophosphate accumulated under these conditions. 5. 5. Polyphosphate accumulation was inhibited by certain amino acid analogs. In C-84, the histidine analog 2-thiazolealanine was found to inhibit RNA degradation but had no effect on the accumulation of polyphosphate. 6. 6. The relationship of polyphosphate accumulation to the primary genetic block is discussed. The possible role of RNA degradation as the immediate cause of polyphosphate accumulation is considered.

The Penetration of Phosphate into Whole and Dissected Amphibian Embryos

ABSTRACT Embryos of Siredon mexicanum and Xenopus laevis were shown, by the use of 32P, to take up small but measurable amounts of phosphate from the culture medium. The rate of uptake was higher in embryos than in unfertilized eggs, and was related to the stage of development. The rate was proportional to the concentration of phosphate in the medium. Spontaneously occurring microcéphalie embryos took up much more phosphate than normal embryos. Injured embryos and dissected fragments of embryos took up more phosphate than intact embryos. Dissected neurulae took up more phosphate than dissected blastulae, and half-gastrulae took up more than either. Vegetative fragments of blastulae took up more phosphate than animal fragments, particularly towards the end of the 6-hour period studied. Ventral fragments of gastrulae took up the same amount of phosphate as dorsal halves during the first 2 hours after cutting, but subsequently took up more. The phosphate uptake of dorsal fragments of neurulae was at first the same as that of ventral fragments, but from 4 to 6 hours after cutting was about twice as rapid. 10 – 4 M p-dinitrophenol had a slight inhibiting effect on uptake of phosphate by whole embryos, counterbalanced by adsorption of 32P on killed cells. The phosphate uptake of fragments was cut down by the inhibitor to about one-half to one-third the level of the controls.