Activation of O(2) Uptake and NAD-Specific Isocitrate Dehydrogenase in Mitochondria Isolated from Cotyledons of Castor Bean by cis, trans-Abscisic Acid |
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Authors: | Tezuka T Yamamoto Y Kondo N |
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Institution: | Department of Agronomy, School of Agriculture, Nagoya University, Chikusa-Ku, Nagoya 464, Japan. |
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Abstract: | The rate of O2 uptake and the activity of NAD-specific isocitrate dehydrogenase (NAD-ICDH) of mitochondria isolated from castor bean cotyledons were increased by added cis, trans-abscisic acid (ABA) in an in vitro system, while the NADP-specific isocitrate dehydrogenase (NADP-ICDH) was not affected by cis, trans-ABA. Trans, trans-ABA showed only a slightly inhibitory effect on O2 uptake. The Vmax value for the isotherm of isocitrate by the enzyme was also increased by cis, trans-ABA. The isocitrate Km value for the enzyme with cis, trans-ABA was calculated to be approximately 249.8 micromolar, while the S0.5 for the enzyme without the ABA was 151.6 micromolar. The n value calculated from the slopes of Hill plots of the reaction velocity of NAD-ICDH against isocitrate concentration was 1.5 in the mitochondrial fraction in the absence of ABA, and cis, trans-ABA treatment decreased the value to 1.0. Cis, trans-ABA also partly overcame the inhibition of NAD-ICDH activity by ATP. |
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