Photoregulation of Carotenoid Biosynthesis in Mutants of Neurospora crassa: Activities of Enzymes Involved in the Synthesis and Conversion of Phytoene

Synthesis o f carotenoids is photoregulated in m any fungi including Neurospora crassa. In order to investigate the regulatory m echanism at the enzym e level, several carotenoid m utants o f Neurospora were used to determ ine the activities o f enzym es involved in the carotenoid b io­ synthetic pathway after growth under illum ination or in darkness. Light stim ulation o f caro­ tenoid form ation was due to enhanced activities o f three subsequent enzym es, geranylgeranyl pyrophosphate synthase, phytoene synthase, and phytoene desaturase indicating a coord inat­ ed regulation at the enzym e level. Farnesyl pyrophosphate synthase and lycopene cyclase were not involved in light regulation. Im m unological studies show ed that in the case o f phytoene desaturase higher activity in the light originated from an increased am ount o f this enzym e in light-grown cultures.