The relationships between quinone and carotenoid in Micrococcus lysodeikticus

Abstract

There are differences between yellow wild-type and white carotenoidless-mutant strains of Micrococcus lysodeikticus, when they are grown in the dark. The white strain exhibits lower viability, quinone levels and respiratory activity of some membrane-bound enzymes. Membrane and cell preparations, of both strains, incorporate [2-14C] mevalonic acid into quinone and also carotenoid in the yellow strain, but labelled isopentenyl pyrophosphate is not incorporated. There is much higher incorporation into quinone in white cells and membranes than yellow. The incorporation in yellow is low, but can be increased, in membranes, by addition of supernatant from the lysis stage of-membrane preparation. Three other carotenoidless mutants obtained, behaved similarly to the strain generally used (strain UVI). Treatment of yellow cells with diphenylamine, which inhibits the synthesis of coloured carotenoids, results in white cultures which exhibits similar properties to strain UVI.

The breakdown of quinone, in differing oxidation-reduction states, has been studied, but difficulties arise as conditions were not found when breakdown was completely independent from synthesis.

Control of synthesis has been studied. Menadione, a possible intermediate in quinone biosynthesis, increases the incorporation of [2-14C] mevalonic acid into quinone, but menaquinone-7 reduces the incorporation.

The effect of inhibitors and substrates of the respiratory chain, on quinone levels and synthesis, was examined. Azide greatly decreases the incorporation of [2-14C] mevalonic acid into quinone.

Malate appears to have only a small effect on quinone, lowering the levels. Under certain conditions, possibly a combination of malate and magnesium concentrations and the state of the membrane, oscillations of quinone levels, in white membranes, are observed.