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Biomedical subjects

F Knüsel

Publications and source records attributed to F Knüsel.

At least 19 recordsLinked to original sources
PubMed1978

Mode of action of quindoxin and substituted quinoxaline-di-N-oxides on Escherichia coli.

The effect of quindoxin on the synthesis of deoxyribonucleic acid (DNA), ribonucleic acid, and protein in Escherichia coli KL 399 was examined under aerobic and anaerobic conditions. In the absence of oxygen the synthesis of DNA was completely inhibited by 10 ppm of quindoxin, whereas the syntheses of ribonucleic acid and protein were not affected. Quinoxalin-di-N-oxides (QdNO) induce degradation of DNA in both proliferating and non-proliferating cells. polA, recA, recB, recC, exrA, and uvrA mutants were more susceptible than the corresponding repair-proficient strains. All strains were more resistant in the presence of oxygen. Quindoxin was reduced to quinoxalin-N-oxide by intact E. coli cells or by a cell-free E. coli extract. Electron spin resonance measurements demonstrated the generation of free radicals during the reduction of quindoxin. Oxygen or deficiency of energy sources impaired the antibiotic activity and the reduction of QdNO. The QdNO reductase activity was demonstrated to be lower in QdNO-resistant mutants than in the susceptible parent strain. Based on these results it is concluded that an intermediate of reduction, probably a free radical, is responsible for the lethal effect of quindoxin. With three independent techniques no evidence has been found for binding of quindoxin to DNA.

Anaerobiosis↗
PubMed1975

[The development and the reversion of spheroplasts of a diaminopimelic acid-auxotrophic mutant of Escherichia coli].

1. The formation and reversion of spheroplasts of the diaminopimelic acid-auxotrophic mutant Escherichia coli K 12, 335, DAP-, R+TEM in a medium lacking diaminopimelic acid have been investigated by microphotography: During their development from rod form cells to spheroplasts cells on slide-surface-agar preparations underwent two successive cell divisions in the course of which the cells retained their rod form. The cells formed by these divisions partitioned into a varying number of spheroplasts of different size. The reversion of spheroplasts to rod form cells, started by the addition of diaminopimelic acid showed two characteristic steps: Each spheroplast partitioned again into several spheroplast-like cell bodies; most of them reverted directly to rod form cells. 2. The release of the R-factor mediated periplasmic TEM-beta-lactamase, E. C. 3.4.2.6., into the growth medium during the development of spheroplasts attained more than 50% of the entire TEM-beta=lactamase activity. The spheroplasts showed a multiple enhancement of TEM-beta-lactamase activity per mg cell protein compared with rod form cells.

Culture Media↗