Early Stages in the Metabolism of Iron 205 



rare and appears to be restricted to the microbial products aspergillic acid, 

 mycobactin and cycloserine. Cycloserine contains O-substituted hydroxyl- 

 amine whereas the two former are N-substituted derivatives. So far as the 

 author is aware, there has been no previous report of the finding of a free 

 hydroxamic acid as a biologically active natural product. 



The hydroxamic acid reaction with ferric ion has found widespread applica- 

 tion in analytical chemistry. Such reactions are usually employed in acidic 

 media where the complex, although highly dissociated, exhibits a deep-red 

 colour with an absorption maximum at about 500 m//. At higher pH the 

 maximum is shifted to lower wavelengths and the colour reaction is less 

 specific. The spectrum of the ferrichrome compounds, on the other hand, is 

 quite insensitive to pH. The maximum for ferrichrome and ferrichrome A 

 remains at 425 and 440 m/^, respectively, even at pH 2. This behaviour may 

 be explained in terms of the strong 'chelate effect' of three binding sites attached 

 to the same molecule. 



Ferrichrome is produced in small amounts by Ustilago sphaerogena even 

 when the organism has been grown in the presence of excess iron. In view of 

 the known ferric ion complexing characteristics of the ferrichromes (Neilands, 

 1957) and of hydroxamic acids in general, a fundamental role for these 

 substances in microbial iron metabolism can be predicted. 



SUMMARY 



1. Itoic acid forms a stable, 3: 1 complex with ferric ion. 



2. The production of itoic acid by B. subtilis is dependent on the iron 

 level of the medium and reaches a maximum at approximately 20 /<g of 

 added iron/1. 



3. The ferric complex of itoic acid is fully available as a source of iron to 

 B. subtilis. 



4. Pre-formed itoic acid is used by the micro-organism following the 

 addition of iron to the medium. 



5. The ferric ion-binding centre of the ferrichrome compounds has been 

 characterized as a hydroxamic acid. 



ADDENDUM 



(.Note added in proof) 

 The acyl moieties have been characterized as three residues each of acetic 

 acid and /ra/zj'-i^-methylglutaconic acid in ferrichrome and ferrichrome A, 

 respectively (Emery and Neilands, 1960). The remaining substituent (R^ or 

 R^i^) is derived from the peptide portion of the molecule (Emery, 1960). 



REFERENCES 



CsAKY, T. Z. (1948). Acta diem. Scand. 2, 450. 



Emery, T. (1960). Doctoral dissertation. University of California, Berkeley. 



Emery, T. &. Neilands, J. B. (1959). Nature, Lond. 184, 1632. 



