SIDEROPHORE ACTIVITY OF MYOINOSITOL HEXAKISPHOSPHATE IN PSEUDOMONAS-AERUGINOSA

myo-Inositol hexakisphosphate (InsP(6)), which is found in soil and mo st, if not all, plant and animal cells, has been estimated to have an affinity for Fe3+ in the range of 10(25) to 10(30) M(-1). In this repo rt, we demonstrate that the Fe-InsP(6) complex has siderophore activit y and is able to reverse the iron-restricted growth inhibition of Pseu domonas aeruginosa by ethylene diamine di(o-hydroxyphenyl)acetic acid. With Fe-55-InsP(6) in transport studies, iron uptake is strongly iron regulated, being repressed after growth in iron-replete conditions an d inhibited by treatment with potassium cyanide and carbonyl cyanide m -chlorophenylhydrazone. The kinetics of iron transport revealed a K-m of 100 nM. Self-displacement of binding of [H-3]InsP(6) to isolated me mbranes by InsP(6) revealed a single class of binding sites (K-d 143 /- 6 nM; Hill coefficient, 1.1 +/- 0.1). The binding of [H-3]InsP(6) t o membranes was not dependent on whether cells had been grown under co nditions of high or low iron concentrations. We believe that this is t he first report of inositol polyphosphate activity in prokaryotic cell s.