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

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.