Referate

Ohne Zusammenfassung     

Referate

Ohne Zusammenfassung     

Referate

Ohne Zusammenfassung     

Referate

Ohne Zusammenfassung     

N- and C-terminal modifications of negamycin

Negamycin 1 is a bactericidal antibiotic with activity against Gram-negative bacteria, and served as a template in an antibiotic discovery program. An orthogonally protected beta-amino acid derivative 3a was synthesized and used in parallel synthesis of negamycin derivatives on solid support. This advanced intermediate was also used for N- and C-terminal modifications using solution-phase methodologies. The N-terminal modifications have resulted in the identification of active analogues, whereas the C-terminal modifications resulted in complete loss of antibacterial activity. The N-methyl negamycin analogue, 19a, inhibits protein synthesis (IC(50)=2.3 microM), has antibacterial activity (Escherichia coli, MIC=16 microgram/mL), and is efficacious in an E. coli murine septicemia model (ED(50)=16.3mg/kg).     

Actinonin, a naturally occurring antibacterial agent, is a potent deformylase inhibitor

Peptide deformylase (PDF) is essential in prokaryotes and absent in mammalian cells, thus making it an attractive target for the discovery of novel antibiotics. We have identified actinonin, a naturally occurring antibacterial agent, as a potent PDF inhibitor. The dissociation constant for this compound was 0.3 x 10(-)(9) M against Ni-PDF from Escherichia coli; the PDF from Staphylococcus aureus gave a similar value. Microbiological evaluation revealed that actinonin is a bacteriostatic agent with activity against Gram-positive and fastidious Gram-negative microorganisms. The PDF gene, def, was placed under control of P(BAD) in E. coli tolC, permitting regulation of PDF expression levels in the cell by varying the external arabinose concentration. The susceptibility of this strain to actinonin increases with decreased levels of PDF expression, indicating that actinonin inhibits bacterial growth by targeting this enzyme. Actinonin provides an excellent starting point from which to derive a more potent PDF inhibitor that has a broader spectrum of antibacterial activity.     

A STUDY OF THE VITAMIN REQUIREMENTS OF THREE SPECIES OF THE GENUS GELASINOSPORA

Hackbarth , R. D., and R. P. Collins . (U. Connecticut, Storrs.) A study of the vitamin requirements of three species of the genus Gelasinospora. Amer. Jour. Bot. 48(7): 603–606. Illus. 1961.—The vitamin requirements of 3 species of Gelasinospora (G. tetrasperma, G. retispora, G. cerealis) were determined. Various combinations of the 10 vitamins used in the study were tried and biotin was found to be the factor limiting growth.     

Phase evaluation in hypothetical receivers simulating ranging in bats

Echo delay discrimination by the bat Eptesicus fuscus had been investigated in an experiment with simulated targets jittering in range (Simmons 1979). The dip in the resulting psychometric curve was used by Simmons to suggest the neuronal implementation of a coherent cross-correlation receiver in the auditory system of bats. By computer simulation it is shown here that the dip may be even more pronounced and less susceptible to noise with alternative receiver configurations which not necessarily evaluate signal phase information coherently, e.g., a bank of neuronal filters with envelope-processing. New behavioral experiments are suggested to critically test such model hypotheses.     

Accuracy of calculated free testosterone differs between equations and depends on gender and SHBG concentration

Serum free testosterone (fT) concentrations are often calculated, however different equations often yield discrepant results. This study explores the sources of this variability. We compared three established and two new equations that differed only by their testosterone association constants with isotope dilution equilibrium dialysis in two patient groups with different gender distributions. Equation components were examined to determine how they impacted correlation with isotope dilution equilibrium dialysis. Association constants derived for each patient group correlated best with isotope dilution equilibrium dialysis for that group and not the other set. Samples with the poorest correlation between isotope dilution equilibrium dialysis and calculated fT results had significantly higher SHBG concentrations. Regardless of equation, ≥25% of samples showed unacceptable deviation from isotope dilution equilibrium dialysis. Association constants and gender makeup and SHBG concentration of the patient groups used to establish an equation all significantly impact correlation with isotope dilution equilibrium dialysis. Application of many fT equations to wider populations will therefore frequently yield results that differ substantially from isotope dilution equilibrium dialysis.