Biosynthesis of valine and isoleucine in plants III. Reductoisomerase of Phaseolus radiatus

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Summary

  • 1.

    The reductoisomerase from Phaseolus radiatus has been partially purified and its properties studied.

  • 2.

    L-Ascorbic acid was found to enhance the rate of reaction when α-aceto-α-hydroxybutyrate was used as the substrate while it has no effect or is slightly inhibitory when α-acetolactate was used as the substrate.

  • 3.

    The optimum pH is around pH 8.6 in Tris-HCl buffer when α-aceto-α-hydroxybutyrate was used as the substrate in the presence of L-ascorbic acid. No definite pH optimum was observed when α-acetolactate was the substrate.

  • 4.

    The Km values for α-aceto-α-hydroxybutyrate and α-acetolactate are 1.2·10−4 M and 5.5·10−3 M respectively.

  • 5.

    No definite involvement of a metal ion could be demonstrated.

  • 6.

    The enzyme is not inbihited by p-hydroxymercuribenzoate, cysteine and 2-mercaptoethanol. Arsenite is slightly inhibitory.

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