Biomedical subjects
Publications and source records attributed to E Boye.
Escherichia coli cells made permeable with a hypotonic tris(hydroxymethyl)aminomethane buffer utilized exogenous deoxyribonucleoside triphosphates to perform semiconservative replication. The rate of replication was the same as in cells made permeable with toluene or sucrose.
The feasibility of flow cytometry for measurements on bacteria has been demonstrated by measurements of DNA-associated fluorescence of Escherichia coli K-12 in various phases of cell growth. Bacteria were stained with a combination of ethidium bromide and mithramycin after fixation in 70% ethanol. Cultures grown to stationary phase accumulated in two peaks representing cells with two and four chromosomes. Qualitatively similar histograms were obtained with cells grown in the presence of chloramphenicol, whereas cells of the temperature sensitive strain E 177 (dnaA) ended up with only one chromosome per cell at the restrictive temperature. The fluorescence intensity of cells with one chromosome was about 10(3) times smaller than that of human diploid cells. Instrumental resolution at this level of intensity was CV = 5%, whereas peak widths corresponded to CV = 7-8%. Dyes bound to RNA did not appear to contribute significantly to the fluorescence.
Induction and repair of double- and single-strand DNA breaks have been measured after decays of 125I and 3H incorporated into the DNA and after external irradiation with 4 MeV electrons. For the decay experiments, cells of wild type Escherichia coli K-12 were superinfected with bacteriophage lambda DNA labelled with 5'-(125I)iodo-2'-deoxyuridine or with (methyl-3H)thymidine and frozen in liquid nitrogen. Aliquots were thawed at intervals and lysed at neutral pH, and the phage DNA was assayed for double- and single-strand breakage by neutral sucrose gradient centrifugation. The gradients used allowed measurements of both kinds of breaks in the same gradient. Decays of 125I induced 0.39 single-strand breaks per double-strand break. No repair of either break type could be detected. Each 3H disintegration caused 0.20 single-strand breaks and very few double-strand breaks. The single-strand breaks were rapidly rejoined after the cells were thawed. For irradiation with 4 MeV electrons, cells of wild type E. coli K-12 were superinfected with phage lambda and suspended in growth medium. Irradiation induced 42 single-strand breaks per double-strand break. The rates of break induction were 6.75 x 10(-14) (double-strand breaks) and 2.82 x 10(-12) (single-strand breaks) per rad and per dalton. The single-strand breaks were rapidly repaired upon incubation whereas the double-strand breaks seemed to remain unrepaired. It is concluded that double-strand breaks in superinfecting bacteriophage lambda DNA are repaired to a very small extent, if at all.
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The anti-angina effect of Verapamil was investigated during a multicentric study carried out with the crossed, double blind technique. The drug was administered in a dose of 240 mg per day per os. During the period of treatment with Verapamil, particularly significant effects in the number of angina attacks, the consumption of nitroglycerin and tolerance of effort were observed.
A brief review is given of the pharmacological data of verapamil, which chemically shows a certain similarity to papaverine. The effect of the drug (80 mg) 3 times daily, on angina pectoris, as compared with placebo, was evaluated in a double-blind cross-over therapeutic trial with 4-wk periods in 47 patients. The incidence of attacks and the nitroglycerine consumption decreased in the second fortnight of the verapamil period by approximately 25% compared with the placebo period. An ergometer test showed a prolongation of the exerice time of 20%. The mean blood pressure and the heart rate fell under verapamil treatment if the patients had values which were relatively high in the placebo period. The increase in heart rate during exercise from two different resting levels showed a tendency to become more pronounced under treatment with verapamil than under placebo. The length of the P-Q intervals were not affected by verapamil. The mechanism of action in angina pectoris is discussed, but it is concluded that it is still not possible to explain it. Twelve Danish medical departments took part in the trial.
The time scale for rejoining of radiation-induced deoxyribonucleic acid (DNA) single-strand breaks was measured in the presence and absence of oxygen. The involvement of DNA polymerase I in this repair process was studied. Formation and rejoining of DNA strand breaks were measured in lambda DNA infecting lysogenic pol(+) and polA1 strains of Escherichia coli irradiated by 4 MeV electrons under identical conditions. Irradiation and transfer to alkaline detergent could be completed in less than 180 ms. The initial yields of DNA strand breaks were identical in pol(+) and polA1 host cells and four- to fivefold higher in the presence of oxygen than in nitrogen anoxia. Evidence for the existence of a very fast repair process, independent of DNA polymerase I, was not found, since no rejoining of radiation-induced DNA strand breaks was observed during incubation from 45 ms to 3 s. In pol(+) host cells most of the strand breaks produced in the presence of oxygen were rejoined within the first 30 to 40 s of incubation, whereas no rejoining could be detected within the same period of time in anoxic cells. Since no rejoining of broken lambda DNA molecules was observed in polA1 host cells, it is concluded that the synthetase activity of DNA polymerase I is involved in the rejoining of DNA breaks induced by radiation in the presence of oxygen.
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