Summary: Association patterns and regulatory properties of chorismate mutase, prephenate dehydratase and prephenate dehydrogenase from ATCC 15926 were studied. Prephenate dehydrogenase (molecular weight 95000) was separated by Sephadex G-100 chromatography from both the chorismate mutase–prephenate dehydratase I complex (molecular weight 75000) and from a second, low molecular weight prephenate dehydratase (prephenate dehydratase II; molecular weight 30000). The chorismate mutase-prephenate dehydratase complex persisted after DEAE-Sephadex A-50 chromatography. With the exception of prephenate dehydratase II, enzyme activities were influenced by end-products. Chorismate mutase was competitively inhibited by -phenylalanine ( = 3·5 μ). Prephenate dehydratase I was inhibited by -phenylalanine ( = 8 μ) and activated by -tyrosine ( = 5 μ). Prephenate dehydrogenase was feedback-inhibited by -tyrosine. Substrate saturation curves of chorismate mutase and of prephenate dehydratase II were hyperbolic with values of 0·31 m for chorismate and 0·015 m for prephenate, respectively. The substrate saturation curve of the complexed prephenate dehydratase I was sigmoid; a value of 0·18 mM was calculated for prephenate. Chorismate mutase, prephenate dehydratase and prephenate dehydrogenase were not repressed by aromatic amino acids.


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