Abstract
Association patterns and regulatory properties of chorismate mutase, prephenate dehydratase and prephenate dehydrogenase from Pseudomonas aureofaciens 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 endproducts. Chorismate mutase was competitively inhibited by L-phenylalanine (Ki=3.5 microM). Prephenate dehydratase I was inhibited by L-phenylalanine (Ki=8 microM) and activated by L-tyrosine (Ka=5 microM). Prephenate dehydrogenase was feedback-inhibited by L-tyrosine. Substrate saturation curves of chorismate mutase and of prephenate dehydratase II were hyperbolic with Km values of 0.31 mM for chorismate and 0.015 mM for prephenate, respectively. The substrate saturation curve of the complexed prephenate dehydratase I was sigmoid; a Km 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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