Studies of the biosynthesis of C50 carotenoids in Halobacterium cutirubrum

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Abstract
Cells of H. cutirubrum were grown in the presence of [14C]mevalonate with and without 3 mM nicotine. Growth of cells was inhibited to a maximum extent of 25% but overall incorporation of 14C into total, neutral, or polar lipids was only inhibited about 16% during active growth and to a much lesser extent or not at all in stationary phase. Little effect of nicotine on labeling of squalenes, vitamin MK-8, geranylgeraniol and phytoene was observed. Labeling of bacterioruberin and monoanhydrobacterioruberin was extensively inhibited while that of lycopene and bisanhydrobacterioruberin was increased reciprocally by growth in the presence of 3 mM nicotine. Reincubation of the labeled nicotine-grown cells in fresh cold medium without nicotine restored the 14C-labeling of bacterioruberin and monoanhydrobacterioruberin at the expense of lycopene and bisanhydrobacterioruberin. These results confirm previous findings suggesting that the C50 bacterioruberin is made by addition of a C5-isoprene unit to each end of the C40-lycopene chain, followed by introduction of 4 hydroxyl groups.

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