202 



J. B. Neilands 



lability of the ferric chelate, it seems very doubtful if this disappearance of 

 itoic acid could be the result of chemical instability of the compound. 



Table 7. Effect of added iron on preformed itoic acid 



PRESENT IN A 36-HR CULTURE OF B. SubtiUs 



The Iron-binding Centre of the Ferrichrome Compounds 



In the Csaky (1948) procedure for free and bound "hydroxylamine", the 

 maximum amount of NHoOH was liberated after a heating period of 12 hr. 

 After correction for destruction of NH2OH during hydrolysis, values very 

 close to 3 moles/mole of iron were found for both ferrichrome and ferri- 

 chrome A (Table 8). 



Table 8. "Hydroxylamine" content of the ferrichrome 

 compounds as determined by acid hydrolysis 



Duplicate samples were heated in 3 n H2SO4 for 12 hr at 100° 



and the liberated NHoOH determined by the method of Csaky 



(1948). A correction of 15 ?„ was applied for destruction of NH^OH 



during hydrolysis 



Ferrichrome 



Ferrichrome A 



/imole NHgOH/yumoIe iron 



2-92, 2-86 



2-94, 3-08 



DISCUSSION 

 The quantity of itoic acid produced by B. subtilis, in excess of 1 //mole/ml, 

 is more than sufficient to complex the total amount of iron available in the 

 special growth medium employed in the present investigation. This fact, in 

 conjunction with the observation that itoic acid prefers to form a 3 : 1 complex 

 with ferric ion, renders it highly probable that this is the initial form of iron 

 that enters into the metabolism of the organism. Further, itoic acid forms 

 a very stable, probably highly specific, complex with ferric ion. In this respect 

 the substance falls into the pattern of other all-oxygen ligands which are well- 

 known to exhibit a marked preference for trivalent iron. The failure of the 

 itoic acid chelate to lose iron as the hydroxide even at very high values of pH 

 is a further indication of the tenacity with which it complexes this metallic ion. 



