The regulation of propionate oxidation in Prototheca zopfii

1. Whole cell suspensions of Prototheca zopfii grown on propionate oxidize propionate, acrylate, malonic semialdehyde and acetate immediately, whereas acetate-grown cells only oxidize acrylate or propionate rapidly after a lag of 20-30min. This adaptation to propionate is slowed down by 8-azaguanine or p-fluorophenylalanine, and is not influenced by adding an ammonium salt or an amino acid mixture. 2. The adaptation involves induction of the enzymes of beta-oxidation of propionate. 3. A small proportion (5-8%) of the activities of propionyl-CoA dehydrogenase, beta-hydroxypropionate dehydrogenase and malonic semialdehyde dehydrogenase are consistently associated with mitochondria isolated from propionate-grown cells. 4. Such mitochondria will oxidize propionyl-CoA, beta-hydroxypropionate and malonic semialdehyde, and the respiration rates with these substrates in the presence of inorganic phosphate are ADP-dependent. 5. Mitochondria from acetate-grown cells do not contain detectable activities of the enzymes of propionate oxidation.

The purification and properties of malonic semialdehyde oxidative decarboxylase from Prototheca zopfii

1. An enzyme, which in the presence of NAD(+) and CoA oxidizes malonic semialdehyde to acetyl-CoA, has been purified from an extract of the colourless alga Prototheca zopfii. 2. The purified enzyme has optimum pH7.5, is specific for NAD(+) and requires a thiol compound for maximum activity. 3. The enzyme is inhibited by arsenite, N-ethylmaleimide and urea. 4. The results are discussed in relation to those obtained by other workers with a similar bacterial enzyme, and a possible reaction sequence is proposed.