CAROTENOIDS 



1/20,000-1/35,000, inhibits carotenoid production in the bacterium 

 Mycobact. phlei {see p. 126). Goodwin 22 has investigated the effect of 

 diphenylamine on carotenogenesis in Phycomyces and found that whilst 

 the production of a-, [3- and y-carotenes and lycopene were almost 

 completely inhibited, that of the more saturated carotenoids, phyto- 

 fluene, phytoene, ^-carotene and neurosporene is considerably 

 increased {see Table 17). These observations suggest two possibilities 

 {a) that p-carotene and lycopene may be built up via saturated inter- 

 mediates, the inhibition by diphenlyamine occurring thus : 



UNKNOWN PRECURSORS > PHYTOENE > PHYTOFLUENE > 



BLOCKED 



^-CAROTENE > MEUROSPORENE > (3-CAROTENE 



HERE 



The second possibility {b) is that the more saturated carotenoids 

 are produced by an independent pathway from the same common 

 precursor as the a-, p- and ycarotenes and lycopene ; blocking of 

 the latter synthesis would then leave more of the common precursor 

 for conversion into phytoene, etc. Much further work is required 

 before a decision can be made as to which possibility is the correct one. 



The mode of action of diphenylamine remains obscure ; an investi- 

 gation into a large number of compounds known to exhibit various 

 types of inhibition has not revealed any with the same action on 

 Phycomyces as diphenylamine. ^ ^a The recent observation of Turian ^ ^^ 

 that in Mycobact. phlei, phenol has the same action as diphenylamine, 

 does not hold with Phycomyces ; neither does his finding that dinitro- 

 phenol enhances carotenogenesis {see also p. 126). Streptomycin 

 inhibits carotene synthesis in Phycomyces. ^ ^a. 



Mutant Studies. Only one investigation on carotenogenesis in fungi 

 has been reported in which mutant strains were examined. Bonner 

 et al. ■* 2 used 7 ultra-violet mutants of Rhodotorula rubra ; the quantita- 

 tive distribution of carotenoids in these mutants are recorded in Table 

 18. These results prompted Bonner et al. to propose the following 

 scheme of carotenoid synthesis in Rhodotorula : 



— ^ P- and y-carotenes 

 Blocked (yellow) 



Unknown precursors > Phytofluene 



in colour- Largely 



less mutants blocked in -> Torulene 



light mutants (red) 



116 



