The manipulation of cellular cytochrome and lipid composition in a haem mutant of Saccharomyces cerevisiae.

1. The ole-3 mutant of Saccharomyces cerevisiae has an early lesion in the pathway of porphyrin biosynthesis. 2. This results in the loss of all haem-containing enzymes, including the mitochondrial cytochromes, and prevents the synthesis of components whose formation requires haem-containing enzymes, including unsaturated fatty acids, ergosterol and methionine. 3. The pleiotropic effects of the primary lesion are reversed by growing mutant ole-3 aerobically in the presence of intermediates of the porphyrin-biosynthetic pathway, and the present work reports the degree of manipulation of lipid and respiratory-cytochrome composition. 4. Supplements of delta-aminolaevulinate in the range 0.5--500 mg/l result in a progressive increase in the cellular content of unsaturated fatty acids and respiratory cytochromes, cause the replacement of lanosterol and squalene by ergosterol, and an increase in total sterol content. 5. Haematoporphyrin and protoporphyrin IX have similar but less extensive effects on cellular composition, whereas haematin allows unsaturated fatty acid synthesis and some sterol synthesis, but has no effect on the formation of respiratory cytochromes. 6. These results suggest that growth of the organism in the presence of defined amounts of delta-aminolaevulinate will be useful in the investigation of the role of lipids and cytochromes in the function and assembly of mitochondrial membranes.