Proteases of Senescing Oat Leaves

Two proteases active in the senescing first leaves of oat seedlings (Avena sativa cv. Victory) have been purified approximately 500-fold by a combination of ammonium sulfate precipitation, affinity chromatography on hemoglobin-Sepharose, and ion exchange chromatography on DEAE-Sephadex. The enzymes show pH optima of 4.2 and 6.6 with denatured hemoglobin as substrate, and the molecular weights of both are about 76,000. Their optimum temperatures are close to 50 C. Small amounts of a third enzyme, active at pH 3.5, may also be present. The enzyme active at pH 6.6 shows evidence of a sulfhydryl residue in the active site.