Stopped-flow kinetic studies of the reaction of barley alpha-amylase/subtilisin inhibitor and the high pI barley alpha-amylasev

Ulrik Sidenius, Karsten Olsen, Birte Svensson, Ulla Christensen

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The interaction of alpha-amylase/subtilisin inhibitor (BASI) from barley seeds and the high pI barley alpha-amylase (AMY2) de novo synthesized during seed germination, has been studied at pH 8.0, 25 degrees C, using stopped-flow fluorescence spectroscopy, equilibrium fluorescence titration and kinetic analysis of the displacement of BASI from the BASI-AMY2 complex by the substrate blue starch. The results are in accordance with a two-step reaction model: [formula: see text] The resulting values of the kinetic parameters were: k2/K1 = (1.0 +/- 0.2) x 10(6) M-1.s-1, K1 = 0.4 +/- 0.21 mM, k2 = 320 +/- 150 s-1, k-2 = (7.2 +/- 0.6) x 10(-5)s-1, and the overall dissociation constant Kd = (0.7 +/- 0.1) x 10(-10) M. BASI thus is best characterized as a fast reacting, tight-binding inhibitor of AMY2.
Original languageEnglish
JournalF E B S Letters
Pages (from-to)250-254
Publication statusPublished - 1995
Externally publishedYes

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