Plant Physiol. Illumina
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Plant Physiology 70:943-948 (1982)
© 1982 American Society of Plant Biologists

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Articles

Isocitrate Lyase from Flax 1

Terminal Residues, Composition, Active Site, and Catalysis

Fazal R. Khan2 and Bruce A. McFadden3

Biochemistry/Biophysics Program and Institute of Biological Chemistry, Washington State University, Pullman, Washington 99164

The cleavage of Ds-isocitrate catalyzed by isocitrate lyase from Linum usitatissimum results in the ordered release of succinate and glyoxylate. The glyoxylate analog 3-bromopyruvate irreversibly inactivates the flax enzyme in a process exhibiting saturation kinetics and protection by glyoxylate or isocitrate or the competitive inhibitor L-tartrate. Succinate provides considerably less protection. Results with 3-bromopyruvate suggest that this reagent modifies plant and prokaryotic isocitrate lyases differently. Treatment of the tetrameric 264,000-dalton flax enzyme with carboxypeptidase A results in a release of one histidine/subunit which is concordant with loss of activity. The only N-terminal residue is methionine. Treatment of flax enzyme with diethylpyrocarbonate at pH 6.5 selectively modifies two histidines per 67,000-dalton subunit. The reaction of one histidine residue is abolished by the binding of L-tartrate and the modification of one is coincident with inactivation. The carboxy-terminal and active-site modifications establish that one histidine residue/monomer is essential in the flax enzyme and considerably extend information heretofore available only for fungal and bacterial isocitrate lyase.

2 Present address: Roche Institute of Molecular Biology, Nutley, NJ 07110.

3 To whom correspondence should be addressed.

1 Supported in part by National Science Foundation Grant PCM 7909786.






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ASPB Publications PLANT PHYSIOLOGY® THE PLANT CELL
Copyright © 1982 by the American Society of Plant Biologists