Fe3+/Fe2+ Mycobactin-Complex Electrochemistry as an Approach to Determine Mycobactin Levels in Urine

Mycobacterium acquire iron by producing siderophores called mycobactins, with an extremely high affinity complexation of Fe3+. The iron complex shows distinctive electrochemistry predicting 18 orders of magnitude greater affinity of the mycobactin for Fe3+ than Fe2+. A heterogeneous standard rate constant, k(s) of the order of 10(-5)cms(-1) confirms quasi reversible electrochemistry and based on the equilibrium in the presence of excess solution Fe3+/Fe2+ the oxidation and reduction peaks for the siderophore complex could be calibrated for ferric mycobactin J (FeMJ). FeMJ spiked urine collected from cows showed a matrix effect on the current peak height. For example, 240 +/- 15 mu M FeMJ was estimated in 600 mu M spiked urine. However, in the presence of excess solution Fe(acac)(3) the same sample yielded an estimated 580 +/- 25 mu M FeMJ.