Plant Physiol.
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Plant Physiology 65:176-183 (1980)
© 1980 American Society of Plant Biologists

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Articles

Comparison of Sensitive and Desensitized Forms of Maize Homoserine Dehydrogenase 1

Cynthia A. Dicamelli2 and John K. Bryan

Department of Biology, Syracuse University, Syracuse, New York 13210, Biological Research Laboratories, Syracuse University, Syracuse, New York 13210

The properties of homoserine dehydrogenase (EC 1.1.1.3) isolated from shoots of young etiolated seedlings of Zea mays L. var. earliking can be reversibly altered by dialysis against an appropriate buffer. Treatment with 500 millimolar potassium phosphate buffer (pH 7.5) in the absence of L-threonine results in diminished regulatory control such that the enzyme becomes less sensitive to feedback inhibition. The physical and regulatory properties of experimentally altered and unaltered enzymes are compared with those of enzyme isolated from shoots of older seedlings. Multiple forms of both sensitive and insensitive enzymes are identified, and a model which is consistent with the observed isozymes and the difference in regulatory properties of enzymes obtained from seedlings of different ages is proposed. The initially sensitive enzyme is postulated to undergo a conformational change followed by formation of insensitive multimeric aggregated forms. The experimental conditions which facilitate alteration of the enzyme are discussed in relation to conditions which could occur in vivo.

2 Current address: Department of Biology, Washington University, St. Louis, Missouri 63130.

1 This project was supported by National Science Foundation Grants PCM 76-03617 and PCM 78-12202 and Syracuse University Senate Research Grants. Taken in part from a thesis submitted in partial fulfillment of the requirements for the Ph.D. by C. A. D.






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Copyright © 1980 by the American Society of Plant Biologists