Iron Storage inMycobacterium smegmatisGrown under Iron-sufficient and Iron-overload Conditions

Abstract

Two kinds of iron-containing proteins the molecular masses of which were about 10 kDa and 24 kDa were isolated from cytoplasmic fractions of Mycobacterium smegmatis grown under iron-sufficient (50 μM Fe) and iron-overload (500 μM Fe) conditions. Based upon the elution profiles in two chromatographic systems, spectrophotometric analysis, and ESR spectrum measurement, the protein of 10 kDa met the criteria for classification as a ferredoxin. Another protein of 24 kDa showed no enzymatic activity, though its detailed structure was unknown. The ferredoxin and the protein of 24 kDa contained about 30% and 50% of the total cellular iron, respectively, when cells were grown under the above conditions. The synthesis of the protein of 24 kDa was, however, completely repressed in cells grown under iron-deficient (0.5 μM Fe) conditions, although the ferredoxin was still synthesized to some extent even in iron-deficient cells. These results suggested that both ferredoxin and the protein of 24 kDa could be synergistic...