Fred E. Hahn

Chloroquine: Physiological Basis of Drug Resistance in Plasmodium berghei

Mouse erythrocytes, parasitized by chloroquine-sensitive plasmodia, concentrate this drug in vivo to levels over twice as high as erythrocytes parasitized by chloroquine-resistant plasmodia; nonparasitized red cells accumulate little chloroquine. Selective toxicity of this drug may depend upon a special drug-concentrating mechanism of plasmodic impairment of such mechanism.

Berberine: complex with DNA.

A complex of calf-thymus DNA with berberine sediments in the analytical ultracentrifuge. The DNA produced systematic changes in the absorption spectrum of berberine which suggest that single alkaloid molecules bind to DNA. Flow dichroism of purines and pyrimidines and of berberine in the complex with DNA had the same signs and magnitudes. Berberine shifted the thermal strand separation profile of DNA to higher temperatures. Therefore, the alkaloid forms a complex with DNA, probably by intercalation.

MODE OF ACTION OF CHLORAMPHENICOL. IX. EFFECTS OF CHLORAMPHENICOL UPON A RIBOSOMAL AMINO ACID POLYMERIZATION SYSTEM AND ITS BINDING TO BACTERIAL RIBOSOME.

Abstract Chloramphenicol at a constant concentration inhibited the polymerization of phenylalanine in a bacterial ribosome-polyuridylic acid system by a constant percentage when graded concentrations of ribosomes, polyuridylic acid, or transfer ribonucleic acid limited the activity of the system. [ 14 C]Cloramphenicol combined weakly but stereospecifically with 70-S ribosomes; the average number of chloramphenicol molecules binding to a ribosome was of the order of 1. The hypothesis is proposed that ribosome-bound chloramphenicol interferes with a function of messenger ribonucleic acid.

DNA: reaction with chloroquine.

Diflerence spectrophotometry shows that double-stranded DNA produces mnarked changes in the absorption spectrum of chloroquine; only minor changes occur with single-stranded DNA. A DNA-chloroquine complex was demonstrated to sediment in the analytical ultracentrifuge. Chloroquine strongly elevated the thermal dissociation temperature, Tm, of DNA. It is concluded that the drug forms a complex with DNA by ionic interaction and stabilizes the helix.

Chloroquine: Mode of Action

The drug chloroquine is bactericidal for Bacillus megaterium; it inhibits DNA and RNA biosynthesis and produces rapid degradation of ribosomes and dissimilation of ribosomal RNA. Inhibition of protein synthesis is also observed, evidently as a secondary effect. Inhibition of DNA replication is proposed as a general mechanism of the antimicrobial action of chloroquine.

Quinacrine (Atebrin): Mode of Action

Quinacrine at a concentration of 8 x 10-4 mole per liter is bactericidal for Escherichia coli, blocks DNA synthesis, and inhibits the syntheses of RNA and protein strongly. At a concentration of 2x 10-4 mole per liter, the drug is bacteriostatic, the syntheses of protein and DNA (but not that of RNA) are partially inhibited, and the bacteria grow into giant filaments. Impairment of DNA replication is proposed as the mode of action of quinacrine.

Interralations between nucleic acid and protein biosynthesis I. Synthesis and fate of bacterial nucleic acids during exposure to, and recovery from the action of chloramphenicol☆

Cells of E. coli B/r, whose protein synthesis is inhibited by chloramphenicol, accumulate several times the amounts of intracellular nucleic acids contained in log-phase bacteria before the onset of chloramphenicol-induced bacteriostasis. Upon removal of chloramphenicol the bacteria pass through a recovery phase during which much of the excess of nucleic acids is ejected from the cells before growth and multiplication are resumed. It is thought that these conditions result from the imbalanced synthesis of normal nucleic acids under the influence of chloramphenicol rather than from the formation and elimination of abnormal polynucleotides.

Erythromycin: Mode of Action

Erythromycin, a specific inhibitor of protein biosynthesis, inhibited the incorporation of phenylalanine by a cell-free ribosomal system prepared from Escherichia coli.

Studies on the complex of distamycin a with calf thymus DNA

The antibiotic, distamycin A (DMC, fig. l), has the unique property of inhibiting induced enzyme synthesis in bacteria [l] . This provides a potential tool in the study of regulatory processes at the gene. DMC alters the melting behavior of calf thymus DNA [2] and inhibits the DNA-dependent RNA and DNA polymerase reactions in vitro [2,3] . These physical and biochemical effects can be attributed to the formation of a complex of DMC with DNA. We report here studies on the complex of DMC with calf thymus DNA and conclude that it has a highly ordered structure.

Interactions of the antibiotic, distamycin A, with native DNA and with synthetic duplex polydeoxyribonucleotides

The complex of distamycin A (DMC) with DNA is very stable: neither dialysis against 1% sodium lauryl sulfate [l] nor treatment with 6 M urea or with physiological concentrations of inorganic ions [2] change the absorption spectrum of bound DMC. The spectrum of the free antibiotic reappeared when NaCIO,, at 7.2 M, was supplied to the DNA-DMC complex. [3]. It is not known whether the effect of ClO, on DNA physically dissociated DMC from DNA or merely altered the conformation of the complex in such a manner that the spectrum changed. We report here a partial restoration of the free antibiotic’s spectrum by enzymatic digestions of the DNA-DMC complex and the complete chemical extraction of the antibiotic from this complex with a biphasic phenolwater system. * Biophysical indicators of DMC’s binding to DNA increase in magnitude with increasing A-T contents of compositionally different DNA’s [3]; it has been suggested that DMC binds preferentially to A-T rich “domains” of DNA [3]. We report here binding studies of DMC to poly d(A-T), poly dA.dT, poly dI.dC and poly dG.dC which show that the presence of guanine, but not that of hypoxanthine, reduced the magnitudes of biophysical indicators of antibiotic binding. DNA-ligand complexes can be broadly categorized into intercalative and non-intercalative structures. We have tested for intercalation of DMC into closed circular DNA viscometrically [4] and conclude that the antibiotic is not intercalated. 2. Materials and methods