Studies in carotenogenesis. 30. The problem of lycopersene formation in Neurospora crassa

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There is evidence that the first tetraterpene formed in carotenoid biosynthesis is not lycopersene, the C40 analogue of squalene, but phytoene (15,15'-dehydrolycopersene). Davies, Goodwin & Mercer (1961) failed to find lycopersene in any carotenogenic system they examined, and it was suggested that lycopersene plays no part in carotenoid biosynthesis (Davies, 1961, 1962; Goodwin, 1961). Mercer, Davies & Goodwin (1963) studied the incorporation of several labelled substrates into higher plant terpenes, but found no evidence for lycopersene being a carotenoid precursor. Anderson & Porter (1962) found that labelled terpenyl pyrophosphates are incorporated into phytoene by tomato and carrot plastids, but no radioactive lycopersene was detected. In fungi, however, although lycopersene is absent from Phycomyces blakesleeanus (B. H. Davies, unpublished work), Grob, Kirschner & Lynen (1961) reported that a system from Neurospora crassa could synthesize radioactive lycopersene from [14C]geranylgeranyl pyrophosphate. Grob & Boschetti (1962) reported that the two major components of a phytoene-free fraction of the total lipid from N. crassa, which had been cultured in the presence of diphenylamine, were squalene and lycopersene. The apparent difference between this and other carotenogenic organisms led to the present investigation into the alleged formation of lycopersene in N. crassa. Carotenoid biosynthesis is partially inhibited by diphenylamine in N. crassa, as in many other carotenogenic micro-organisms (see Goodwin, 1959). This inhibition results in the accumulation of the more saturated C40 polyenes, phytoene, phytofluene, 6-carotene and neurosporene (Turian & Haxo, 1952; Turian, 1957; Zalokar, 1957). If lycopersene were concerned in carotenoid biosynthesis, it would probably accumulate along with phytoene, etc. in diphenylamine-inhibited cultures.