Drechsel H, Thieken A, Reissbrodt R, Jung G, Winkelmann G
Institut für Organische Chemie, Universität Tübingen, Germany.
J Bacteriol. 1993 May;175(9):2727-33. doi: 10.1128/jb.175.9.2727-2733.1993.
Growth promotion and iron transport studies revealed that certain alpha-keto acids generated by amino acid deaminases, by enterobacteria of the Proteus-Providencia-Morganella group (of the tribe Proteeae), show significant siderophore activity. Their iron-binding properties were confirmed by the chrome azurol S assay and UV spectra. These compounds form ligand-to-metal charge transfer bands in the range of 400 to 500 nm. Additional absorption bands of the enolized ligands at 500 to 700 nm are responsible for color formation. Siderophore activity was most pronounced with alpha-keto acids possessing an aromatic or heteroaromatic side chain, like phenylpyruvic acid and indolylpyruvic acid, resulting from deamination of phenylalanine and tryptophan, respectively. In addition, alpha-keto acids possessing longer nonpolar side chains, like alpha-ketoisocaproic acid or alpha-ketoisovaleric acid and even alpha-ketoadipic acid, also showed siderophore activity which was absent or negligible with smaller alpha-keto acids or those possessing polar functional groups, like pyruvic acid, alpha-ketobutyric acid, or alpha-ketoglutaric acid. The fact that deaminase-negative enterobacteria, like Escherichia coli and Salmonella spp., could not utilize alpha-keto acids supports the view that specific iron-carboxylate transport systems have evolved in members of the tribe Proteeae and are designed to recognize ferric complexes of both alpha-hydroxy acids and alpha-keto acids, of which the latter can easily be generated by L-amino acid deaminases in an amino acid-rich medium. Exogenous siderophores, like ferric hydroxamates (ferrichromes) and ferric polycarboxylates (rhizoferrin and citrate), were also utilized by members of the tribe Proteeae.
生长促进和铁转运研究表明，由变形杆菌-普罗威登斯菌-摩根菌属（变形杆菌族）的肠道细菌通过氨基酸脱氨酶产生的某些α-酮酸具有显著的铁载体活性。铬天青S测定法和紫外光谱证实了它们的铁结合特性。这些化合物在400至500nm范围内形成配体-金属电荷转移带。烯醇化配体在500至700nm处的额外吸收带导致颜色形成。铁载体活性在具有芳香或杂芳香侧链的α-酮酸中最为明显，如苯丙酮酸和吲哚丙酮酸，它们分别由苯丙氨酸和色氨酸脱氨产生。此外，具有较长非极性侧链的α-酮酸，如α-酮异己酸或α-酮异戊酸，甚至α-酮己二酸，也表现出铁载体活性，而较小的α-酮酸或具有极性官能团的α-酮酸，如丙酮酸、α-酮丁酸或α-酮戊二酸，则不存在或铁载体活性可忽略不计。脱氨酶阴性的肠道细菌，如大肠杆菌和沙门氏菌属，不能利用α-酮酸这一事实支持了这样一种观点，即变形杆菌族成员已经进化出特定的铁-羧酸盐转运系统，该系统旨在识别α-羟基酸和α-酮酸的铁络合物，其中后者可以在富含氨基酸的培养基中由L-氨基酸脱氨酶轻易产生。变形杆菌族成员也利用外源性铁载体，如高铁氧肟酸盐（铁色素）和高铁多羧酸盐（根铁素和柠檬酸盐）。
