In vitro carotenogenesis by wild type and mutants of Phycomyces blakesleeanus

Abstract

Cell extracts from shake cultures of the wild type and six mutant strains of Phycomyces converted [2- 14 C] MVA into carotenes, squalene and prenyl phosphates. Oxygen was required for the desaturation of phytoene. When compared with the wild type, cells extracts of carB and carR mutants are much less effective in phytoene dehydrogenation and lycopene cyclization, respectively. This confirms previous conclusions about the biochemical functions of the carB and carR genes, which were based on genetic and in vivo studies. CarA strain mutants accumulate, in vivo , much less β-carotene than the wild type. This correlates with a 10-fold decrease in carotenogenesis in vitro . The addition of retinol to incubations of cell extracts of the wild type and C2 strains stimulated β-carotene formation. Both carB and carR mutants show enhanced total carotenogenic activities in vitro and the carS mutant shows a higher β-carotene-synthesizing activity than the wild type. It is suggested that the feed-back regulatory mechanism known to control this pathway operates at the level of enzyme synthesis.