Monzyk B, Crumbliss A L
J Inorg Biochem. 1983 Aug;19(1):19-39. doi: 10.1016/0162-0134(83)85010-7.
Deferriferrioxamine B (H3DFB) is a linear trihydroxamic acid siderophore with molecular formula NH2(CH2)5[N(OH)C(O)(CH2)2C(O)NH(CH2)5]2N(OH)C(O)CH3 that forms a kinetically and thermodynamically stable complex with iron(III), ferrioxamine B. Under the conditions of our study (pH = 4.30, 25 degrees C), ferrioxamine B, Fe(HDFB)+, is hexacoordinated and the terminal amine group is protonated. Addition of simple hydroxamic acids, R1C(O)N(OH)R2 (R1 = CH3, R2 = H; R1 = C6H5, R2 = H; R1 = R2 = CH3), to an aqueous solution of ferrioxamine B at pH = 4.30, 25.0 degrees C, I = 2.0, results in the formation of ternary complexes Fe(H2DFB)A+ and Fe(H3DFB)A2+, and tris complexes FeA3, where A- represents the bidendate hydroxamate anion R1C(O)N(O)R2-. The addition of a molar excess of ethylenediaminetetraacetic acid (EDTA) to an aqueous solution of ferrioxamine B at pH 4.30 results in a slow exchange of iron(III) to eventually completely form Fe(EDTA)- and H4DFB+. The addition of a hydroxamic acid, HA, catalyzes the rate of this iron exchange reaction: (formula; see text) A four parallel path mechanism is proposed for reaction (1) in which catalysis occurs via transient formation of the ternary and tris complexes Fe(H2DFB) A+, Fe(H3DFB)A2+, and FeA3. Rate and equilibrium constants for the various reaction paths to products were obtained and the influence of hydroxamic acid structure on catalytic efficiency is discussed. The importance of a low energy pathway for iron dissociation from a siderophore complex in influencing microbial iron bio-availability is discussed. The system represented by reaction (1) is proposed as a possible model for in vivo catalyzed release of iron from its siderophore complex at the cell wall or interior, where EDTA represents the intracellular storage depot or membrane-bound carrier and HA represents a low molecular weight hydroxamate-based metabolite capable of catalyzing interligand iron exchange.
去铁胺B（H3DFB）是一种线性三异羟肟酸铁载体，分子式为NH2(CH2)5[N(OH)C(O)(CH2)2C(O)NH(CH2)5]2N(OH)C(O)CH3，它与铁（III）形成动力学和热力学稳定的配合物——去铁胺B。在我们的研究条件下（pH = 4.30，25℃），去铁胺B，即Fe(HDFB)+，是六配位的，末端胺基被质子化。在pH = 4.30、25.0℃、离子强度I = 2.0的条件下，向去铁胺B的水溶液中加入简单的异羟肟酸R1C(O)N(OH)R2（R1 = CH3，R2 = H；R1 = C6H5，R2 = H；R1 = R2 = CH3），会形成三元配合物Fe(H2DFB)A+和Fe(H3DFB)A2+，以及三配合物FeA3，其中A-代表双齿异羟肟酸根阴离子R1C(O)N(O)R2-。在pH 4.30时，向去铁胺B的水溶液中加入摩尔过量的乙二胺四乙酸（EDTA），会导致铁（III）缓慢交换，最终完全形成Fe(EDTA)-和H4DFB+。加入异羟肟酸HA会催化这种铁交换反应的速率：（公式；见原文）针对反应（1）提出了一种四平行路径机制，其中催化作用是通过三元和三配合物Fe(H2DFB) A+、Fe(H3DFB)A2+和FeA3的瞬态形成来实现的。获得了各种反应路径生成产物的速率和平衡常数，并讨论了异羟肟酸结构对催化效率的影响。讨论了铁从铁载体配合物解离的低能量途径对微生物铁生物可利用性的影响。反应（1）所代表的体系被提议作为一种可能的模型，用于体内在细胞壁或细胞内部催化铁从其铁载体配合物中释放，其中EDTA代表细胞内储存库或膜结合载体，HA代表能够催化配体间铁交换的低分子量异羟肟酸基代谢物。
