Evidence for increased proton dissociation in low-activity forms of dephosphorylated squash-leaf nitrate reductase.
The pH dependence of squash-leaf nitrate reductase has been studied. It has been found that high- and low-activity forms of purified nitrate reductase (both forms dephosphorylated) have different optimum pH values. A high-activity form has always a higher pH optimum compared with a low-activity form. Model computations show that the decrease in activity and the corresponding change of the pH optimum is apparently due to a conformation-dependent increase of proton dissociation of the enzyme. As previously shown, this behavior is also observed in leaf extracts during the conversion (and probably phosphorylation of nitrate reductase) from a high-active form to a low-active form when plants are transferred from light to darkness.
Ruoff
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Stavanger College, School of Technology and Science, P.O. Box 2557 Ullandhaug, 4004 Stavanger, Rogaland, Norway.
Lillo
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