Two new cysteine endopeptidases obtained from the latex of Araujia hortorum fruits

Abstract

Two new endopeptidases were purified to homogeneity from the latex of Araujia hortorum fruits by a simple purification procedure involving ultracentrifugation and ion exchange chromatography. Molecular weights of araujiain h II and araujiain h III were 23,718 and 23546 (mass spectrometry), respectively. The isoelectric point of araujiain h II was 8.9, whereas araujiain h III had a pI higher than 9.3. Maximum proteolytic activity on caseine was reached at pH 8.0-9.0 for both endopeptidases, which were irreversibly inhibited by iodoacetate and E-64, suggesting they belong to the cysteine protease family. Esterolytic activity was determined on N-alpha-CBZ-amino acid-p-nitrophenyl esters, and the highest kcat/Km values for the both enzymes were obtained with the glutamine derivative. The N-terminal sequences of araujiain h II and araujiain h III showed a high degree of homology with other plant cysteine endopeptidases.