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Metabolism of trans-Aconitic Acid in Maize : II. Regulatory Properties of Two Compartmented Forms of Citrate Dehydrase |
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| Authors: | Brauer D Teel M R |
| Affiliation: | Department of Plant Science, University of Delaware, Newark, Delaware 19711. |
| Abstract: | Kinetics of two molecular forms of K-dependent citrate dehydrase in maize (Zea mays L.) are reported. The isozymes, designated CD I and CD II, were found to be compartmented in mitochondria and cytosol, respectively. CD I exhibited hyperbolic kinetics with respect to both citrate and potassium with Km 2.3 and 12 millimolar, respectively. Maximum velocity was 0.38 micromole of trans-aconitic acid per minute per milligram protein. The pH optimum was 7.2. trans-aconitic synthesis by CD I is regulated by both citrate concentration and pH. CD II exhibited hyperbolic kinetics with respect to citrate (Km 0.6 millimolar) but sigmoidal kinetics with respect to potassium. trans-aconitic acid synthesis by CD II is regulated by potassium. This may account for the positive correlation between leaf potassium and trans-aconitic acid in certain grasses (Clark 1968 Crop Sci 8: 165). |
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