Geranylgeranyl pyrophosphate as the condensing unit for enzymatic synthesis of carotenes

Abstract

A cell-free enzyme system capable of converting 4,8,12,16- trans- 14C-geranylgeranyl pyrophosphate into phytoene, phytofluene, ζ-carotene, neurosporene, and lycopene was obtained from a Phycomyces blakesleeanus R 1 mutant. The conditions of incubation and cofactor requirements for the conversion were defined. The incorporation of radioactive substrate into carotenes was maximal at pH 7·8 with Tris-HCl buffer and in the presence of a sulfhydryl reagent (dithiothreitol) at 25° for 24 hr. Geranylgeranyl pyrophosphate was a much more effective precursor than mevalonic acid in this system and it was demonstrated that geranylgeranyl pyrophosphate is the condensing unit for carotene biosynthesis.