Ligand-induced interconversions of maize homoserine dehydrogenase among different states

Archives of Biochemistry and Biophysics
S Krishnaswamy, J K Bryan

Abstract

The threonine-sensitive homoserine dehydrogenase has been isolated and extensively purified from shoots of Zea mays L. var. earliking. This enzyme is shown to be hysteretic under certain conditions. Progress curves of the NAD-dependent reaction catalyzed by the maize enzyme can be characterized by distinct lags prior to achievement of steady state velocities, reflecting transitions from less active species to a more active steady state form of the enzyme. Incubation of the enzyme for 1 min at 25 degrees C prior to initiation of the reaction profoundly influences the properties of the less active enzyme and the nature of the subsequent slow transitions during assay. When the feedback modifier, L-threonine, or KCl is included in the preincubation mixture, the transitions involve biomolecular association reactions. In the absence of either ligand, or in the presence of an appropriate mixture of both, a unimolecular transition occurs during assay. Three unique preincubation states of the enzyme have been identified on the basis of their response to substrates and effectors; whereas, the kinetic and regulatory properties of the steady state form of the enzyme are independent of preincubation conditions. Steady state can thus be achi...Continue Reading

References

Dec 1, 1978·Archives of Biochemistry and Biophysics·B P Yip, F B Rudolph
Jul 1, 1982·Archives of Biochemistry and Biophysics·I E Woodrow, D A Walker
Feb 1, 1980·Plant Physiology·C A Dicamelli, J K Bryan
Jul 1, 1981·Plant Physiology·L Rayder, I P Ting
Dec 1, 1981·Plant Physiology·R T WeddingM K Black

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Citations

Nov 1, 1983·Archives of Biochemistry and Biophysics·S Krishnaswamy, J K Bryan
Nov 1, 1994·TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik·G J MuehlbauerC M Donovan

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