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Enterobactin (also known as enterochelin) is a high affinity siderophore that acquires iron for microbial systems. It is primarily found in Gram-negative bacteria, such as Escherichia coli and Salmonella typhimurium.
Enterobactin is the strongest siderophore known, binding to the ferric ion (Fe3+) with affinity K = 1052 M−1. This value is substantially larger than even some synthetic metal , such as EDTA (Kf,Fe3+ ~ 1025 M−1). Due to its high affinity, enterobactin is capable of chelation even in environments where the concentration of ferric ion is held very low, such as within living organisms. bacteria can steal iron from other living organisms using this mechanism, even though the concentration of iron is kept extremely low due to the toxicity of free iron.
Due to the extreme iron binding affinity of enterobactin, it is necessary to cleave FeEnt with ferrienterobactin esterase to remove the iron. This degradation yields three 2,3-dihydroxybenzoyl-L-serine units. redox of the iron (Fe3+ to Fe2+) occurs in conjunction with this cleavage, but no FeEnt bacterial reductase enzyme has been identified, and the mechanism for this process is still unclear. The reduction potential for Fe3+/Fe2+–enterobactin complex is pH dependent and varies from −0.57 V (vs NHE) at pH 6 to −0.79 V at pH 7.4 to −0.99 at pH values higher than 10.4.
Enterobactin has also been shown to have roles in the host, including mammals. Enterobactin is considered a hallmark for pathogenic infection that is sequestered by mammalian protein lipocalin 2 in an attempt to starve the infectious bacteria for iron. In contrast, it has also been shown that supplementation with both Ent and FeEnt can benefit the host directly and promote iron uptake in C. elegans and mammalian cultured cells.
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