ABSTRACT: A proteinaceous inhibitor with high activity against papain was found in seeds of the xerophytic algaroba tree (Prosopis julifora). The proteinase inhibitor Pj was purified using Sephacryl S-200 gel filtration followed by reverse-phase high-performance liquid chromatography on a Vidac 18 TP. Inhibitor Pj showed a Mr of 20,000 on sodium dodecyl sulfate-polyacrylamide gel electrophoresis and a Mr of 19.2K by mass spectrometry. The inhibition of papain by the Pj inhibitor was the noncompetitive type, with a Ki value of 0.59 × 10−9 M. The gelatinase activity of papain was strongly inhibited by Pj too. The N-terminal amino acid sequence of the Pj inhibitor showed homology with the N-terminal amino acid sequence of the Kunitz-proteinase inhibitor family. Pj was strongly effective against digestive proteinases from bean weevil Acanthoscelides obtectus and cowpea weevil Callosobruchus maculatus and was moderately active toward midgut proteinases from pod weevil Mimosestes mimosae and Mexican bean weevil Zabrotes subfasciatus. The data shown here suggest that the protein present in algaroba seeds is involved with defense responses to insects and may be an important tool to be used in engineering plants resistant to bean weevils.
Pesticide Biochemistry and Physiology.