Inactivation of bacteriophages by decay of incorporated radioactive phosphorus

The inactivation of the phages T1, T2, T3, T5, T7, and λ by decay of incorporated P³² has been studied. It was found that these phages fall into two classes of sensitivity to P³² decay: at the same specific activity of P³² in their deoxyribonucleic acid (DNA), T2 and T5 are inactivated three times as rapidly as T1, T3, T7, and λ. Since the strains of the first class were found to contain about three times as much total phosphorus per phage particle as those of the second) it appears that the fraction of all P³² disintegrations which are lethal is very nearly the same in all the strains. This fraction α depends on the temperature at which decay is allowed to proceed, being 0.05 at –196°C., 0.1 at +4°C., and 0.3 at 65°C. Decay of P³² taking place only after the penetration of the DNA of a radioactive phage particle into the interior of the bacterial cell can still prevent the reproduction of the parental phage, albeit inactivation now proceeds at a slightly reduced rate. T2 phages inactivated by decay of P³² can be cross-reactivated; i.e., donate some of their genetic characters to the progeny of a mixed infection with a non-radioactive phage. They do not, however, exhibit any multiplicity reactivation or photoreactivation. The fact that at low temperatures less than one-tenth of the P³² disintegrations are lethal to the phage particle and the dependence of the fraction of lethal disintegrations on temperature can be accounted for by the double stranded structure of the DNA macromolecule.

Tumours of the skin and other delayed effects of external beta irradiation of mice using 90Sr and 32P

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Leukocyte labeling with inorganic radiophosphorus

Plasma clearance of inorganic P32 given in a single intravenous injection has been evaluated. Significant levels of activity persist for at least 7 days following injection of only 2 µc/kg. Inorganic P32 uptake into various fractions of circulating leukocytes and into fractions of marrow cells has been studied. In marrow cells, equilibration of extracellular phosphate and intracellular acid-soluble organic and inorganic phosphates appears to be reached by 24 hr and probably occurs sooner. In leukocytes thought to be postmitotic at the time label is injected this equilibrium is not reached until 48 hr. In rabbits the postmitotic maturation pool is sufficient to replace circulating leukocytes for at least 48 hr; this defines the time required for cell passage through this pool under normal conditions. Significant deoxyribonucleic acid tagging from a single intravenous injection of P32 appears to proceed for several days.