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A yellow-green, fluorescent siderophore A3 was extracellularly produced under iron-limited growth conditions from Pseudomnnas synxantha A3. The physicochemical and biological properties of siderophore A3 were examined. The approximate molecular weights of the Fe(1H)-siderophore A3-1 complex and Fe(III)-siderophore A3-2 complex were estimated to be about 1,300 and 1,100, respectively, by Bio-gel P2 gel exclusion chromatography. The molar ratio between the siderophore and the Fe(I1T) was 1.08 mole. The molecular weight of the complex could be calculated with this ratio and the new values were 1,150 and 960, respectively. The binding constant(K) between the siderophore A3 and Fe(III) that determined by displacing the iron from the Fe(III)-siderophore complex with EDTA was 4.12X 10´" at pH 5.0. Siderophore A3 appeared to have antibacterial activity on several bacterial strains, however, ferric siderophore A3 complex did not show that activity. The cytotoxicity of siderophore A3 was obtained from Human Chronic Myelogenous Leukemia K562 cells. Inhibition concentration (50%)(ICs") was 0.17 pg/ml.
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