Abstract
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.