Specificity of siderophore receptors in membrane vesicles of Bacillus megaterium

J E Aswell, A H Haydon, H R Turner, C A Dawkins, J E Arceneaux
1977 Journal of Bacteriology  
Membrane vesicles ofBacillus megaterium strains SK11 and Ardl bound the ferrischizokinen and ferriferrioxamine B siderophores (iron transport cofactors). An approximately equimolar uptake of both labels of [3H, 59Fe]ferrischizokinen indicated binding of the intact chelate. Binding reached equilibrium in 2 to 5 min, was temperature independent, and was unaltered by the addition of several energy sources. A 91% dissociation of bound [59Fe]ferrischizokinen was achieved in 60 s by the addition of
more » ... y the addition of excess ferrischizokinen. Ferriaerobactin, a siderophore which is structurally related to ferrischizokinen, caused no detectable release of bound [59Fe]ferrischizokinen. Of several other ferrihydroxamates tested, only ferriferrichrome A achieved the release (11%) of [59Fe]ferrischizokinen. Rapid dissociation (92%) of bound [59Fe]ferriferrioxamine B by the addition of ferriferrioxamine B was observed, and a 67% release of [59Fe]ferriferrioxamine B was caused by ferriA22765, its structural relative. Ferrischizokinen, ferriferrichrome A, and ferrirhodotorulic acid produced a 6, 25, and 29% dissociation, respectively, of [59Fe]ferriferrioxamine B; ferriaerobactin caused no dissociation. [59Felferriaerobactin was bound by the membranes, but its dissociation was not effected by unlabeled ferriaerobactin, suggesting no specific receptors for this chelate. The respective binding affinity constants and maximal binding capacities of membrane vesicles of strain SK1l were 2 x 107 M-' and 280 pmol per mg of protein for ferrischizokinen and 7 x 107 M-1 and 37 pmol per mg of protein for ferriferrioxamine B. These values in strain Ardl were, respectively, 1.4 x 107 M-' and 186 pmol per mg of protein for ferrischizokinen and 11 x 107 M-' and 23 pmol per mg of protein for ferriferrioxamine B. Separate, specific binding sites (receptors) for ferrischizokinen and ferriferrioxamine B exist on the vesicles. The ferrischizokinen receptors have a lower affinity but a higher binding capacity (eightfold) than that shown by the ferriferrioxamine B receptor. These receptors may be components of independent transport systems. on May 9, 2020 by guest
doi:10.1128/jb.130.1.173-180.1977 fatcat:j6vme6ubcvbgvaogdt5575v5zi