Siderophores schizokinen

H. A. Akers, Isolation of the siderophore schizokinen from. soil of rice field. Appl. Environ. Microbiol. 45 1704 (1983). 

Cyanobacteria were probably the first organisms to perform oxygenic photosynthesis resulting eventually in the oxidation of environmental Fe " to Fe " with all its consequences. To cope with this problem the production of siderophores was initiated. Not much is known about the siderophores of cyanobacteria. Schizokinen (see below under citrate siderophores, Sect. 4.1) (326) found to be produced by several bacterial species may have been acquired by gene transfer see however also the citrate siderophores synechobactins. 

The schizokinen-mediated Fe " transport in Bacillus megaterium was studied by double labelling with e and (8). At 37°C, uptake of Fe and of are parallel during the first 30 sec, then that of e continues until it levels off after 2 min, while that of [ H]-schizokinen drops to a low constant level. At 0°C, uptake of both labels reaches this low level which is obviously due to the binding of the ferri-siderophore to the cell surface. At 37°C, transport into the cell, release of iron, and re-export of the ligand follow. Apparently a shuttle mechanism takes place, cf. the experimental results obtained with parabactin (Sect. 3.2) indicative of a taxi mechanism. 

Budzikiewicz H, Kilz S, Taraz K, Meyer JM (1997) Identical Pyoverdines from Pseudomonas fluorescens 9AW and from Pseudomonas putida 9BW. Z Naturforsch 52c 721 Budzikiewicz H, Miinzinger M, Taraz K, Meyer JM (1997) Schizokinen, the Siderophore of the Plant Deleterious Bacterium Ralstonia (Pseudomonas) solanacearum ATCC 11969. Z Naturforsch 52c 496... 

Plowman JE, Loehr TM, Goldman SJ, Sanders-Loehr J (1984) Stmcture and Siderophore Activity of Ferric Schizokinen. J Inorg Biochem 20 183... 

Storey EP, Boghozian R, Little JL, Lowman DW, Charkraborty R (2006) Characterization of Schizokinen a Dfliydroxamate-type Siderophore Produced by Rhizobium legumino-sarum lARI 917. BioMetals 19 637... 

Siderophores with citrate-hydroxamate structures (schizokinen, arthrobactin and aerobactin) are synthesized by enteric bacilli and Arthrobacter spp. Their structures are shown in Figure 48. 

The kinetic lability of ferric siderophores requires that transport experiments be performed with molecules bearing separate radioactive labels in the metal and ligand moieties. As coordination compounds the siderophores are thermodynamically stable and kinetically labile. The formation constants are typically 1030. In the case of ferrichrome the exchange half time at pH 6.3 and 37° is about 10 min (57). Published work (58, 59) with doubly labeled ferric schizokinen in Bacillus mega-terium and ferric aerobactin in A. aerogenes as well as a study of ferric enterobactin in E. coli (60) in each instance suggests a synchronous uptake mechanism for iron and ligand. 

The ferrichromes, fusarinines, and ferrioxamines are typical trihydroxamate siderophores, while enterobactin is a cyclic tricatecholate siderophore. However, there are several exceptions which employ mixed forms of coordination. For example, aero-bactin, schizokinen and arthrobactin contain, in addition to two hydroxamate groups, a a-hydroxy-carboxylate unit which completes the hexadentate ligand structure 30). The recently isolated ferrioxamine H, with two hydroxamate and one carboxylate, is only pentadentate — the sixth coordination site presumably occupied by water 31). 

Three other metals, namely, copper, vanadium, and molybdenium, possess appreciable affinities for siderophores. It is possible that siderophores or siderophore-like molecules are involved in the microbial transport of these metals. Copper(II) forms stable complexes with hydroxamate siderophores (for instance, schizokinen, desferriox-amine B. and desfeirithiocin) and catechol siderophores (for instance, enterobactin). However, copper(II), unlike iron(III), also possesses a high affinity for amino acids and small peptides, and this property renders it unlikely that copper uptake is dependent on siderophore-medi-ated transport. 

Structure of marine cyanobacterial siderophores has not been reported until recently. Synechobactins (21) are the first structurally elucidated siderophores from marine cyanobacteria [55] and are related to schizokinen isolated from freshwater cyanobacteria [56]. Synechobactins were isolated from the supernatant of the coastal marine cyanobacterium Synechococcus sp. Although they are not heterocycles, they are included in this review because... 

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