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Partial Purification and Characterization of a Phytochrome-degrading Neutral Protease from Etiolated Oat Shoots ¹

^a The Biological Laboratories, Harvard University, Cambridge, Massachusetts 02138

A factor catalyzing the in vitro degradation of oat phytochrome in crude extracts has been shown to be a proteolytic enzyme. The enzyme, an endoprotease, has been purified about 600-fold from dark-grown oat shoots by chromatography on ion exchange and molecular seive gels. The pH-activity curve is broad, with a maximum around pH 6.4. The enzyme is apparently dependent on the presence of reduced sulfhydryl groups for activity: low concentrations of reductants stimulate it, while inhibition has been obtained with a variety of sulfhydryl antagonists. High ionic strength conditions are inhibitory. A molecular weight of 61,500 has been estimated, though autolysis may yield smaller active fragments. An enzyme with similar properties has been isolated from imbibed oat seeds, light-grown oat shoots, and dark-grown rye shoots.

¹ Supported by grants from the National Science Foundation (GB-6683 and GB-15572), Research Corporation, and E. I. duPont de Nemours and Co. to W. R. B. and a National Science Foundation Predoctoral Fellowship to C. S. P.