Cation conductance and efflux induced by polyene antibiotics in the membrane of skeletal muscle fiber.
(25/28)
Cation conductance and efflux induced by polyene antibiotics amphotericin B (AMB), amphotericin B methyl ester (AME), nystatin, mycoheptin, and levorin on frog isolated skeletal muscle fibers and whole sartorius muscles were investigated. Conductance was measured under current-clamp conditions using a double sucrose-gap technique. Cation efflux was studied using flame emission photometry. Some new data were obtained concerning the effects of levorin and mycoheptin on biological membranes. The power dependence of polyene-induced cation transport on antibiotic concentration in muscle membrane was lower than that in bilayers. The decline in the equilibrium conductance caused by polyene removal (except for levorin) was very fast. There was reverse temperature dependence of AMB- and nystatin-induced conductances. Both induced conductance and efflux values demonstrated a correlation with the order of antifungal activities: levorin > AMB, mycoheptin > AME > nystatin, except for AME, which was more potent on yeastlike cells. These effects were interpreted in terms of possible differences in the kinetics of channel formation in biological and model membranes and in light of the role of nonconducting antibiotic forms in biological membranes. (+info)
Factors affecting the production of candicidin.
(26/28)
Factors affecting candicidin synthesis and mycelial growth of Streptomyces griseus IMRU 3570 were studied. Inorganic phosphate was found to inhibit candicidin synthesis but to stimulate mycelial growth. Zinc, iron, and magnesium ions stimulated candicidin synthesis at relatively high concentrations in a complex medium but not in a synthetic medium. No other factors studied, such as temperature, oxygen absorption rate, and sugar concentration, were found to differentially affect antibiotic synthesis and mycelial growth. Optimum concentration of inorganic phosphate for candicidin synthesis in a chemically defined medium was found to be between 5 x 10(-5) and 5 x 10(-4) M. The culture in idiophase stage can be reverted to typical trophophase growth by the addition of inorganic phosphate, suggesting the controlling role of inorganic phosphate in repression and derepression of secondary metabolic and primary metabolic activity of the culture. With a soya peptone-glucose medium, the maximum rate of candicidin production could be maintained and extended for a considerable length of time by controlling the culture pH at 8.0, using glucose to adjust the pH during the later stages of a batch fermentation. Carrying out fermentations in this way has given candicidin yields up to 4 g/liter. (+info)
Rapid incorporation of precursors into candicidin by resting cells of Streptomyces griseus.
(27/28)
Labeled acetate, propionate and p-aminobenzoic acid were efficiently incorporated into candicidin by phosphate-limited resting cells of Streptomyces griseus. The efficiency of incorporation in short-term experiments using phosphate-limited resting cells was similar to that achieved previously in long-term experiments using growing cells. (2-14C)Propionate was more efficiently incorpoated than (1-14C)propionate, (U-14C)propionate, or (U-14C)-acetate. p-Aminobenzoic acid incorporation is linear over a 10-hour period while those of acetate or propionate reach a constant level after approximately 4 hours of incubation. Double-labeled candicidin of high specific activity was prepared by supplementing the resting cell system with (3H)acetate and (14C)p-aminobenzoic acid. (+info)
A role for pabAB, a p-aminobenzoate synthase gene of Streptomyces venezuelae ISP5230, in chloramphenicol biosynthesis.
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Mutagenesis of Streptomyces venezuelae ISP5230 and selection for P-aminobenzoic acid-dependent growth in the presence of sulfanilamide yielded pab mutants (VS519 and VS620) that continued to produce chloramphenicol (Cm), although with increased medium dependence. Transforming the mutants with pDQ102 or pDQ103, which carried a pab-complementing fragment from S. venezuelae ISP5230 in alternative orientations, restored uniformly high Cm production in VS620, but did not alter the medium dependence of Cm production in VS519. The cloned S. venezuelae DNA fragment was subcloned and trimmed to the minimum size conferring pab complementation. The resulting 2.8 kb BamHl-Sacl fragment was sequenced. Codon preference analysis showed one complete ORF encoding a polypeptide of 670 amino acids. Comparison of the deduced amino acid sequence with database proteins indicated that the N- and C-terminal regions resembled PabA and PabB, respectively, of numerous bacteria. The gene product showed overall sequence similarity to the product of a fused pabAB gene associated with secondary metabolism in Streptomyces griseus. Insertion of an apramycin resistance gene into pabAB cloned in a segregationally unstable vector and replacement of the S. venezuelae chromosomal pabAB with the disrupted copy lowered sulfanilamide resistance from 25 to 5 micrograms mL-1 and blocked Cm production. (+info)