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Plant Physiology 70:723-727 (1982)
© 1982 American Society of Plant Biologists

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Articles

Metabolism of trans-Aconitic Acid in Maize 1

II. Regulatory Properties of Two Compartmented Forms of Citrate Dehydrase

David Brauer2 and Merle R. Teel

Department of Plant Science, University of Delaware, Newark, Delaware 19711

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).

2 Present address: Agronomy Department, University of Kentucky Lexington, KY 40506

1 Published with the approval of the Director of the Delaware Agricultural Experiment Station as Miscellaneous Paper No. 973. Contribution No. 117 of the Department of Plant Science.






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Copyright © 1982 by the American Society of Plant Biologists