Species and Environmental Variations in the Effect of Inorganic Phosphate on Sucrose-Phosphate Synthase Activity

Open Access
Publisher Website
Google Scholar
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.