Mode of Action of Antibiotic U-20,661

Antibiotic U-20,661 was shown to inhibit predominantly deoxyribonucleic acid (DNA)-directed ribonucleic acid (RNA) synthesis by binding to the double-stranded DNA template. Specific binding to DNA was verified by difference spectroscopy, reversal of the RNA polymerase inhibitory effect by increasing concentrations of DNA template, and by moderately increasing the melting temperature of double-stranded DNA in the presence of the antibiotic. The RNA polymerase reaction primed with synthetic poly dAT was inhibited considerably, but not completely even with high concentrations of antibiotic. Thus, the agent might bind to adenine or thymidine or both bases in the double-stranded DNA helix.     

New antibacterial agent (U-24,544) isolated from Streptomyces griseus

Antibiotic U-24,544 is a new agent isolated from the culture broth of a streptomycete strain. The antibiotic inhibits a variety of gram-positive and gram-negative bacteria in vitro, but is ineffective in treatment of experimental bacterial infections in mice. It is fairly cytotoxic in mammalian cell cultures and remarkably nontoxic in mice.     

Mode of Action of the Antibiotic Siccanin on Intact Cells and Mitochondria of Trichophyton mentagrophytes

Siccanin at 3 mug/ml completely inhibited the growth of Trichophyton mentagrophytes. The primary site of action of siccanin on T. mentagrophytes is succinate dehydrogenase in the terminal electron transport system. At a concentration of siccanin giving 50% inhibition of growth (0.3 mug/ml), respiration of intact cells was inhibited more strongly than any other cellular functions tested, including the syntheses of cellular ribonucleic acid, deoxyribonucleic acid, phospholipid, protein, and cell wall fractions. In addition, at the same concentration siccanin did not cause any detectable damage in the permeability of the cells. Furthermore, the oxidation of succinate in mitochondrial preparation is more sensitive to the antibiotic than respiration in intact cells. Oxidation of other substrates tested was less sensitive to siccanin than that of succinate. The antibiotic inhibited both phosphorylation and oxidation, without causing changes in the P:O ratio. Siccanin at 0.03 mug/ml, which caused 50% inhibition of succinate oxidation in mitochondria, had effect neither on the exchange reaction between inorganic phosphate (P(i)) and adenosine triphosphate (ATP) nor on that between adenosine diphosphate and ATP. An ATP phosphohydrolase activity was also insensitive to the antibiotic. At very high concentrations, however, the antibiotic slightly inhibited the P(i)-ATP exchange reaction. From those results, it was concluded that siccanin inhibits fungal growth by inhibiting the respiratory electron transport system.     

Differential Effects of Monovalent and Divalent Ions upon the Mode of Action of the Polyene Antibiotic Candicidin

The polyene antibiotic candicidin is a potent membrane active agent, the action of which can be inhibited by the presence of certain ions. The destruction of the selective permeability of yeast membranes by candicidin allows small molecules to leak into the environment. Loss of intracellular potassium ions inhibits yeast glycolysis. This inhibition may be reversed by extracellular concentrations of potassium or ammonium ions. Monovalent ions did not prevent antibiotic absorption or protect yeast growth from the action of the antibiotic. Divalent ions did not protect yeast glycolysis from the action of candicidin, but were able to reduce antibiotic-induced membrane damage and allowed yeast growth in the presence of antibiotic. It is suggested that divalent ions may interact with membrane sterols creating steric hindrance to subsequent candicidin absorption.     

Uncoupling Action of Antibiotic Sporaviridins with Rat-liver Mitochondria

The effects of the glycoside antibiotic sporaviridins (SVDs) on oxidative phosphorylation of rat-liver mitochondria were examined. SVDs released state 4 respiration, dissipated transmembrane electrical potential, and accelerated ATPase activity. These facts demonstrated that SVDs are potent uncouplers of oxidative phosphorylation. During the uncoupling caused by SVDs, large amplitude swelling and oxidation of intramitochondrial NAD(P)H occurred, suggesting that SVDs greatly enhanced nonspecific permeability of the inner mitochondrial membrane. It is suggested that the uncoupling action of SVDs might be caused by dissipation of proton electrochemical potential due to an increase in the permeability of inner mitochondrial membrane.     

U-21,963, a New Antibiotic: II. Isolation and Characterization

The isolation and characterization of antibiotic U-21,963 are discussed. This compound is a highly unsaturated monobasic acid with the molecular formula C(9)H(7)NO(3). The molecular weight is 177. It is dextrorotatory, [alpha](D) = +138 degrees , and has a pK(a) of 5.1. The ultraviolet absorption spectrum, which showed a maximum at 223 mmu (epsilon = 15,115), indicates unsaturation alpha-beta to the carboxyl group, and the infrared spectrum suggests the presence of an acetylenic group. Explosive decomposition of U-21,963 at 97 C conforms with the latter. U-21,963 is relatively insoluble in water, but readily soluble in ethyl alcohol, acetone, and halogenated hydrocarbons.     

Mode of Action of Lomofungin

Lomofungin inhibited the growth of some yeasts and mycelial fungi at concentrations between 5 and 10 μg/ml. At such concentrations, there was no decrease in endogenous and exogenous oxygen consumption, and even 50 μg of antibiotic per ml caused only slight decreases. The permeation of the cell membrane was changed so that leakage of ninhydrin-positive substances was reduced, and the uptake of ¹⁴C-labeled glucose, amino acids, uracil, and thymidine was decreased at concentrations as low as 4 μg/ml. Protein synthesis in whole cells of Saccharomyces cerevisiae was reduced 35% at 10 μg/ml. However, the antibiotic did not reduce the incorporation of phenylalanine-U-¹⁴C into polypeptides with cell-free systems of Rhizoctonia solani and S. cerevisiae. The synthesis of ribonucleic acid (RNA) and deoxyribonucleic acid (DNA) was inhibited even at concentrations of lomofungin of 4 μg/ml. Since RNA synthesis was inhibited at lower concentrations and earlier than DNA synthesis, the primary site of action of the antibiotic appears to be the synthesis of RNA.     

Mode of Action of Zorbamycin

Zorbamycin (U-30,604E) induces rapid degradation of deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) in Bacillus subtilis cells. DNA degradation is initiated first and is closely followed by the degradation of RNA. No interaction between isolated DNA and zorbamycin is observed. Nucleic acid and protein syntheses are not inhibited by zorbamycin in cell-free systems. Since the initial effect of the antibiotic is expressed at the level of the cellular DNA fraction, we assume that zorbamycin somehow induces a change in the structure or function of the cellular DNA fraction which results in rapid breakdown of this fraction.     

Mode of Action of Vibriocin

The mechanism of action of vibriocin, a bacteriocin produced by Vibrio comma, was investigated. Its lethal action (as defined by the loss in colony-forming ability) was reversed by tryptic digestion within 7 to 10 min after adsorption. The bacteriocin had a pronounced inhibitory effect on deoxyribonucleic acid (DNA) synthesis, whereas ribonucleic acid (RNA) and protein synthesis continued, although at a reduced rate. Chloramphenicol protected sensitive bacteria from the lethal action. Degradation of bacterial DNA prelabeled with (3)H-thymidine, as measured by changes in acid-precipitable radioactivity, occurred 10 min after treatment with vibriocin. The bacteriocin per se had no detectable deoxyribonuclease activity. Observation of vibriocin-treated cells by phase-contrast microscopy, measurement of ultraviolet light-absorbing capacity of extracellular fluid, and (42)K-efflux studies indicated a damaged bacterial membrane. This impairment of membrane function occurred in the presence of chloramphenicol and thus, unlike the lethal effect of vibriocin, was independent of protein synthesis.     

Mode of Action of Streptozotocin

Streptozotocin induces rapid degradation of deoxyribonucleic acid (DNA) in actively dividing or resting Bacillus subtilis cells. Difference spectroscopy showed that the antibiotic interacts specifically with cytosine containing mononucleotides in vitro. This interference occurs only within the very narrow pH range of 5 to 5.5 and is reversed immediately upon lowering or increasing the pH. No measurable interaction was observed between isolated DNA and streptozotocin. The possibility is discussed that interaction of streptozotocin with cytosine residues in cellular DNA, although possibly taking place at a very low frequency, may constitute the primary step inducing DNA strand breakage.     

Mode of Action of Lomofungin

Lomofungin inhibited the growth of some yeasts and mycelial fungi at concentrations between 5 and 10 μg/ml. At such concentrations, there was no decrease in endogenous and exogenous oxygen consumption, and even 50 μg of antibiotic per ml caused only slight decreases. The permeation of the cell membrane was changed so that leakage of ninhydrin-positive substances was reduced, and the uptake of ¹⁴C-labeled glucose, amino acids, uracil, and thymidine was decreased at concentrations as low as 4 μg/ml. Protein synthesis in whole cells of Saccharomyces cerevisiae was reduced 35% at 10 μg/ml. However, the antibiotic did not reduce the incorporation of phenylalanine-U-¹⁴C into polypeptides with cell-free systems of Rhizoctonia solani and S. cerevisiae. The synthesis of ribonucleic acid (RNA) and deoxyribonucleic acid (DNA) was inhibited even at concentrations of lomofungin of 4 μg/ml. Since RNA synthesis was inhibited at lower concentrations and earlier than DNA synthesis, the primary site of action of the antibiotic appears to be the synthesis of RNA.     

U-21,963, a New Antibiotic: I. Discovery and Biological Activity

A new antibiotic, U-21,963, is produced by a new strain of Trichoderma viride. Antibiotic activity can be demonstrated against both gram-positive and gram-negative bacteria and also against a wide variety of fungi. U-21,963 is not cross-resistant with other commonly used antibiotics. U-21,963 afforded no protection against Klebsiella pneumoniae, Streptococcus pyogenes, or Staphylococcus aureus when it was injected subcutaneously into mice.     

Mode of Action of Antirheumatic Drugs

The concentrations of free and protein-bound L-tryptophan were measured in sera from normal subjects, patients with rheumatoid arthritis, pregnant women, and patients with jaundice. In the patients with rheumatoid arthritis receiving treatment with one or more antirheumatic drugs the percentage of the amino-acid bound to the circulating proteins was significantly depressed and in one patient returned to normal when therapy was stopped. Pregnancy and jaundice were also associated with raised free tryptophan and decreased bound tryptophan concentrations and bilirubin displaced the amino-acid from its binding sites on human serum proteins in vitro. It is suggested the behaviour of tryptophan mimics that of certain peptides which protect susceptible tissues against chronic inflammatory insults.