Cobalt toxicity and iron metabolism in Neurospora crassa

1. Increasing concentrations of cobalt in the medium result in increased production of an iron-binding compound and a corresponding fall in catalase activity of Neurospora crassa. 2. Cobalt rapidly depletes the medium of iron by enhancing the rate of iron uptake by the mycelium. 3. With toxic amounts of cobalt there is a fall in bound (59)Fe and haem (59)Fe as well as a decreased incorporation of [2-(14)C]glycine into the mycelial haem fraction. The production of the iron-binding compound precedes the fall in the iron-dependent systems mentioned. 4. The (59)Fe bound to the iron-binding compound acts as a better iron source for haem synthesis in cell-free extracts as compared with (59)FeSO(4). 5. Cobalt inhibits iron incorporation into protoporphyrin in cell-free extracts but is not itself incorporated to an appreciable extent.