The effects of iron-limited growth on the reduced nicotinamide-adenine dinucleotide dehydrogenase activity and the membrane proteins of Candida utilis mitochondria.

1. The mitochondrial NADH dehydrogenase (EC 1.6.99.3) of Candida utilis exhibited altered properties when the organism was grown under iron-limited conditions. No suitable acceptor was found for assay of this enzyme from iron-limited cells. 2. Mitochondrial membrane proteins from C. utilis were analysed by polyacrylamide-gel electrophoresis. Compared with glycerol-limited cells, iron limitation resulted in the loss of at least two polypeptides from the mitochondrial membrane. 3. Neither of the polypeptides affected by iron limitation was part of a cytochrome, although one of them was part of the mitochondrial NADH dehydrogenase. 4. Non-haem iron of mitochondrial membranes was released in the presence of sodium dodecyl sulphate, and electrophoresis in solutions of this detergent cannot be used directly to identify iron-sulphur proteins. Non-ionic detergents do not release non-haem iron but nor do they provide a satisfactory system for electrophoretic separation.