Inhibition of carotenogenesis in cell-free systems of Aphanocapsa and Phycomyces

Abstract

A number of herbicides have been identified as inhibitors of carotene biosynthesis. Because of the multiple effects associated with inhibition of carotenogenesis in vivo. it was considered opportune to investigate the effects of such compounds on carotene biosynthesis in cell free systems. The carotenogenic cell free system from Phycomyces blakesleeanus was optimized with respect to concentrations of NAD+, NADP , ATP, Mg2+ and Mn2+ . A new photosynthetically active, carotenogenic cell extract from Aphanocapsa that incorporates radioactivity from [2-14C] GGPP], was discovered and the cofactor requirements elucidated. The preparation from Aphanocapsa was used to investigate the structure-bleaching activity relationship of (i) a series of norflurazon and difunone derivatives with respect to phenyl ring substitution; (ii) a series of alkyl phenoxy-benzamides with respect to alkyl chain and phenoxy ring substitution. Selected alkyl phenoxy benzamides were also tested with the Phycomyces system. The Phycomyces extract was used to investigate the effects of a number of diphenyl compounds, e.g. diphenylamine, on in vivo carotenogenesis. Selected diphenyl compounds were tested against the Aphanocapsa system. A hypothetical mechanism for the inhibitory action of alkyl phenoxybenzamides and diphenyl compounds is discussed and a hypothesis forwarded to explain the super accumulation of radioactivity into phytoene under certain circumstances.