Propionate assimilation in the flagellate Polytomella caeca. An inducible mitochondrial enzyme system

1. The assimilation of propionate by Polytomella caeca involves the β-oxidation of this fatty acid. 2. Propionate-grown cells immediately oxidize propionate, β-hydroxypropionate, malonic semialdehyde and acetate; acetate-grown cells oxidize propionate rapidly only after a lag of 2hr., and this adaptation of resting cells to propionate involves the formation of the enzymes of β-oxidation. 3. The β-hydroxypropionate dehydrogenase and malonic semialdehyde dehydrogenase activities of both propionate-grown and propionate-adapted cells are partly located in mitochondrial fractions. 4. Mitochondria isolated from propionate-grown cells, and also those from acetate-grown cells fully adapted to propionate, oxidize succinate, α-oxoglutarate, β-hydroxypropionate and malonic semialdehyde; oxidation of these substrates is tightly coupled to the phosphorylation of ADP. 5. Mitochondria from acetate-grown cells exhibit ADP-dependent oxidation of succinate and α-oxoglutarate, but do not oxidize β-hydroxypropionate or malonic semialdehyde. Mitochondria isolated from acetate-grown cells adapted to propionate for 5hr. slowly oxidize β-hydroxypropionate and malonic semialdehyde, but no tightly coupled phosphorylation is detectable. 6. Two of the inducible enzymes of propionate oxidation are located within the NAD-impermeable barrier and appear to be membrane-bound. 7. The formation of the inducible enzymes is inhibited by cycloheximide and actinomycin D, but not by chloramphenicol.