Neutral peptidases in the stroma of pea chloroplasts |
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Authors: | Liu X Q Jagendorf A T |
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Affiliation: | Plant Biology Section, Cornell University, Ithaca, New York 14853. |
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Abstract: | One endopeptidase (EP1) and at least three aminopeptidases (AP1, AP2, and AP3) were discovered in the stroma of chloroplasts isolated from pea seedlings (Pisum sativum L.), and purified over 100-fold. EP1 requires added Mg2+ or Ca2+ for activity, may have an additional tightly bound metal atom, and is inhibited by sulfhydryl reagents but not by serine residue-directed inhibitors. It is reversibly inhibited by dithiothreitol. Its specificity is for the bond between two adjacent Ala or Gly residues. Its molecular mass is 93 kilodaltons, estimated on a gel filtration column. Aminopeptidase activities were detected with the aid of different amino acyl-β-naphthylamides as substrates. They were resolved into at least three individual proteins by gel filtration and DEAE-cellulose chromatography, having apparent molecular masses of 269,000 (AP1), 84,000 (AP2), and 42,000 (AP3) daltons, respectively. Each has a unique specificity for substrates, with AP1 hydrolyzing only the Prolyl-β-naphthylamide. None of the APs require added divalent cations for activity, but the possibility of a tightly bound metal function was suggested in AP2 and AP3 (not AP1) from effects of inhibitors. A probable sulfhydryl residue function was indicated for all three, from inhibition by p-hydroxymercuribenzoate and Zn2+. All these peptidases had pH optima at 7.7. |
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