Ferri-enterobactin

The transport system of Bacillus subtilis accommodates the Fe " complexes of enterobactin (A-configured), enanfio-D-enterobactin and of corynebactin (bacilli-bactin) (both A). Since only A complexes can be bound to the receptor a configurational change from A to A is induced. Only the natural ferri-L-siderophores can be degraded enzymatically (399, 408). 

Figure 1. Schematic of the two iron transport systems of microorganisms. The high affinity system is comprised of specific carriers of ferric ion (siderophores) and their cognate membrane hound receptors. Both components of the system are regulated by iron repression through a mechanism which is still poorly understood. The high affinity system is invoked only when the available iron supply is limiting otherwise iron enters the cell via a nonspecific, low affinity uptake system. Ferri-chrome apparently delivers its iron by simple reduction. In contrasty the tricatechol siderophore enterobactin may require both reduction and ligand hydrolysis for release...

In common with most prokaryotes, many fungi have siderophore-dependent iron uptake systems. The ferri-chrome-type siderophores are often employed, although other types of siderophore are also used. Indeed, even if, like the quintessential scavenger baker s yeast (Saccharomyces cerevisiae), they produce no siderophores of their own, they nonetheless have several distinct facilitators for the uptake of ferric siderophores, including ferric enterobactin, which is produced by many bacteria, but not by fungi. 

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