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Nodule extracts prepared from Glycine max var Woodworth possessed endopeptidase, aminoptidase, and carboxypeptidase actiities. Three distinct endopeptidase activities could be resolved by disc-gel electrophoresis at pH 8.8. According to their order of increasing electrophoretic mobility, the first of these enzymes hydrolyzed azocasein and n-benzoyl-LLeu-p8-naphthylamide, while the second hydrolyzed n-benzoyl-L-Arg-/8-, and azocasein. The third endopeptidase hydrolyzed Bz-L-Arg-8NA, Bz-L-Arg-pNA, and hemoglobin. Fractions of these enzymes extracted from electrophoresis gels were shown to have pH optima from 7.5 to 9.8.AU of the endopeptidases were completely inhibited by diisopropylphosphorofluoridate, demonstrating that they were serine proteases.Aminopeptidase activity was measured using amino acyl-p-naphthylamides. Electrophoresis of nodule extracts at pH 6.8 resolved the aminopeptidase activity of nodule extracts into at least four fractions based on mobility and on activities toward amino acyl-pi-naphthylamides. The major activity of two of the aminopeptidases was directed toward L-Leu-and LMet-p-naphthylamide, while the other two aminopeptidases exhibited broader specificity and were capable of hydrolyzing a large number of amino acyl-.-naphthylamides. Two of the aminopeptidases extracted from electrophoresis gels were classiffed as thiol type enzymes, and all four aminopeptidases had neutral to basic pH optima.Senescence of soybean root nodules results in a decreased capacity to reduce atmospheric nitrogen, thus potentially limiting the supply of amino nitrogen to the plant. After the decline in nitrogenase activity, total soluble protein per unit fresh weight of nodule decreases rapidly (22), although the fresh weight per nodule shows little change. In addition, the total number of nodules per plant decreases sharply. Thus, nodule senescence can be characterized by a sharp decline in nitrogenase activity coupled with a degeneration of the nodule leading to loss of soluble protein and eventual abscission of the nodule from the root. The loss of soluble protein is a characteristic feature of all types of plant senescence, and is generally attributed to increased activity of proteolytic enzymes. The role of proteolytic enzymes in nodule senescence is not as well established as in leaf senescence (7, 8, 19, '

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