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Phytochemistry. 2009 Jul-Aug;70(11-12):1374-81. doi: 10.1016/j.phytochem.2009.08.009. Epub 2009 Sep 16.

Characterization of a highly stable trypsin-like proteinase inhibitor from the seeds of Opuntia streptacantha (O. streptacantha Lemaire).

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Centro de Investigación y de Estudios Avanzados del I.P.N., Unidad Irapuato, Km. 9.6, Libramiento Norte Carr., Irapuato-León A. P. 629, Irapuato, Gto. 36821, Mexico.


A trypsin inhibitor from Opuntia streptacantha Lemaire (Prickly pear) seeds was purified and characterized. Of several proteases tested, this inhibitor showed specificity to trypsin-like enzymes. The major inhibitor present in these seeds showed distinctive characteristics, most notably a low molecular weight of 4.19 kDa, as determined by MALDI TOF, and an unusually high thermal stability, retaining most of the activity after heating the sample 1h to 120 degrees C with a pressure of 1 kg/cm(2). Its complete amino acid sequence was obtained through mass spectrometry, this establishing presence a blocked N-terminal region. When comparing its sequence in the MEROPS database for peptidases and peptidase inhibitors, it showed 34.48% identity with a serine-proteinase inhibitor from the I15 family.

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