Analysis of microsomal flavoproteins from Phycomyces sporangiophores: Candidates for the blue-light photoreceptor

To help identify components of the blue-light photoreceptor system for phototropism in Phycomyces blakesleeanus Bgff., proteins from a microsomal fraction obtained from synchronous sporangiophores were studied. By two-dimensional gel electrophoresis, two proteins (FP₁, FP₂) with covalently bound flavins were found. FP₁ has a molecular weight of 71 000 and an isoelectric point of 6.6; FP₂ has a molecular weight of 59 000 and an isoelectric point of 6.5. These flavoproteins were purified by column chromatography and gel filtration while assaying for flavins by fluorescence. The relative concentrations of FP₁ and FP₂ were affected by light applied during growth. These flavoproteins are likely components of the blue-light photoreceptor complex mediating phototropism in Phycomyces.