SOME ASPECTS OF MICROBIAL IRON METABOLISM

Abstract

INTRODUCTION (7). A comparison of some of the properties of In recent years it has become evident that the the fungal and beef heart cytochrome c follows: total iron content of the animal organism is greater than the sum of the iron found in all of the Hemochrome Absorption known iron compounds (1). The nature of this Source M8,D pI Maxima (mp) remaining iron is unknown although in part it a may be accounted for by the "non-heme iron" which Green and Beinert (2) have discovU. sphaerogena.... 18-20 X 103 7.0 550 520 ered as components of various respiratory Beef heart.12 X 103 10.5 550 520 enzymes. It is apparent that, eventually, all of the iron compounds of living cells will have to be On a molar basis the beef heart and fungal cytoidentified before a total picture of iron metabolism chromes were found to be of about equal activity and function can be established. Since all living in the rat liver succinoxidase system. cells are faced with more or less similar metabolic Ferrichrome. Extracts of U. sphaerogena from problems it should be possible to use almost any which all cytochrome components had been respecies as a subject for the study of unknown moved by ammonium sulfate precipitation still iron compounds. On the other hand, as Kluyver contained an appreciable amount of both color and van Niel have pointed out in their elegant and iron. These extracts were accordingly fraclittle book The Microbe's Contribution to Biology tionated by solvent extraction, and a crystalline (3), there are certain advantages in the selection iron containing substance named ferrichrome was of microorganisms as subjects for the examinaobtained (8). Crystals of this substance are tion of metabolic processes. Thus it is possible shown in figure 1. that an organism could be found with an exagIn the production of ferrichrome, U. sphaerogerated iron metabolism. After studying this gena was grown in 200-liter batches using vigorous species it might further be possible to apply the aeration and a medium containing yeast extract results to the general problem of iron metabolism and glucose. The yield of pigment was 0.4 to 0.5 in plants and animals. g per kg of dried cells. The isolation of ferrichrome from the culture fluid has not been achieved. EXPERIMENTS WITH USTILAGO SPHAEROGENA Ferrichrome is also formed by U. sphaerogena Ustilago cytochrome c. The smut fungus Ustilago when the fungus is grown on a simple salts-glucose sphaerogena is an organism with an exaggerated medium (9). With such a medium the ferrichrome iron metabolism. Weisel and Allen (4) showed concentration within the cells has been increased that when grown on a medium containing yeast to about 1.5 g per kg of dried cells in the absence extract, this fungus formed large amounts of a of added zinc (9). substance which by direct spectrophotometric Chemical properties of ferrichrome. The purity examination of the cells appeared to be cytoof thrice recrystallized ferrichrome can be conchrome c. In subsequent work they found that veniently checked by paper chromatography, the addition of zinc to a simple synthetic medium using ultraviolet inspection. The Rf values are was an important factor in the realization of high 0.40 and 0.68 with a butanol-acetic acid-water yields of the hemoprotein (5). and with a 50 per cent methanol-0.1 M phosphate In order to be certain that the substance obbuffer solvent system, respectively. Thus the served by Weisel and Allen was indeed cytosubstance is extremely soluble in water and chrome c, the pigment was extracted from the sparingly soluble in all organic solvents with the cells and obtained in the pure state (6) by use of exception of hot methanol. an ion exchange chromatography procedure preThe approximate empirical formula is C27-29 viously worked out for beef heart cvtochrome c H42 46012N9Fe. The mol wt of ferrichrome has