Siderophores porphyrins

Metallothioneins, Phytochelatins, Siderophores, Porphyrins 1-2 Low Very strong ... 

FIGURE 7 Examples of Fe ligands. (A) The bacterial hexadentate siderophore enterobactin. (B) The planar porphyrin phytochelatin. M denotes the metal binding site. Reprinted with permission from Stumm W., and J. J. Morgan. 1996. Aquatic Chemistry Chemical Equilibria and Rates in Natural Waters. Copyright 1996 Wiley, New York. 

The general properties of siderophores have been described extensively (2), and up-to-date lists of the individual compounds, their sources from aerobic and facultative aerobic species, and their properties have been published (3,4, 5). (Porphyrin Products, P. O. Box 31, Logan, UT 84321, sell a limited number of siderophores.) The earlier literature on iron assimilation by microbes, including enteric species, may be found elsewhere (6,7). For information on the chemical constitution and physiological role of the outer membrane of enteric bacteria, the reader is referred to Nakae and Nikaido (8). 

Figure 38 5 Short term Fe uptake rates from model iron/ligand complexes hy Trichodesmium colonies collected in the suhtropical Atlantic Ocean. Shown are uptake rates from Fe complexed to a trihydroxamate siderophore (desferrioxamine), a dihydroxamate siderophore (rhodoturulic acid), and a porphyrin (protoporphyrin IX). For comparative purposes, uptake rates were also measured using added inorganic Fe (111). Achilles et al. (2003), Limnology and Oceanography 48 2250-2255.

Besides the siderophores, the menaquinone pathway also involves isochorismate synthase (review [100]). Menaquinone (vitamin K2) is an electron carrier involved in anaerobic ATP-generating redox reactions. It also plays a role in the anaerobic biosynthesis of pyrimidines, porphyrins and succinyl CoA [101-104]. Menaquinone is detectable in E. call. The accumulation of menaquinone (MK8) is significantly stimulated in the absence of oxygen. 

---