Pyrimidine biosynthesis in Serratia marcescens: Polypeptide interactions of three nonsequential enzymes |
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Authors: | James R Wild William L Belser |
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Institution: | (1) Department of Biology, University of California, Riverside, California;(2) Present address: Genetics Section, Texas A&M University, College Station, Texas |
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Abstract: | Orotidine-5 -monophosphate pyrophosphorylase (OMPppase, E.C. 2.4.2.10) and orotidylate decarboxylase (OMPdecase, E.C. 4.1.1.23) were purified from Serratia marcescens HY. These enzymes required physical association for maximal catalytic activities and formed a fragile complex with dihydroorotase (DHOase, E.C. 3.5.2.3.). OMPppase reversibly lost 50% of its activity upon separation from DHOase. The kinetic characteristics of OMPppase were modified by this separation. In the presence of DHOase, the K
ms for PRPP and orotate were stoichiometric: 2.3×10–6
m and 2.6×10–6
m, respectively. Following separation, the K
ms were significantly different: 1.3 × 10–6
m for PRPP and 4.1×10–6
m for orotate. OMPppase and OMPdecase could be reversibly separated by acrylamide gel electrophoresis, but the separation was accompanied by a loss of catalytic efficiency for both enzymes. DHOase readily associated into multiple molecular forms and could not be purified. The DHOase-OMPppase-OMPdecase interactions demonstrate that a weakly aggregated, multifunctional enzyme complex participates in the biosynthesis of pyrimidine nucleotides in S. marcescens. This unique association of nonsequential biosynthetic enzymes may represent a larger complex which provides a channeling or regulatory unit.This work was supported by grants from the National Science Foundation (NSF GB 5811) and the Office of Naval Research (Nonr 4413). One of us (J.W.) was a National Science Foundation Graduate Fellow. |
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Keywords: | Serratia marcescens pyrimidine biosynthesis enzyme aggregation regulation bacteria |
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