Characterization of the proteinase that initiates the degradation of the trypsin inhibitor in germinating mung beans (Vigna radiata)

• Published in: Plant physiology (Bethesda) Vol. 84; no. 1; pp. 93 - 98
• Main Authors: Wilson, K.A, Tan-Wilson, A.L
• Format: Journal Article
• Language: English
• Published: Rockville, MD American Society of Plant Physiologists 01.05.1987
• Subjects: ACTIVIDAD ENZIMATICA; ACTIVITE ENZYMATIQUE; Agronomy. Soil science and plant productions; Biological and medical sciences; Cotyledons; Economic plant physiology; ENZYME INHIBITORS; Enzymes; ENZYMIC ACTIVITY; EPURATION; Esters; Formates; Fractionation; Fundamental and applied biological sciences. Psychology; Gels; GERMINACION; GERMINATION; INHIBIDORES DE ENZIMAS; INHIBITEUR D'ENZYME; Metabolism; Nutrition. Photosynthesis. Respiration. Metabolism; Plant physiology and development; Plants; PROTEASAS; PROTEASE; PROTEASES; PROTEINAS; PROTEINE; PROTEINS; PROTEOLISIS; PROTEOLYSE; PROTEOLYSIS; PURIFICACION; PURIFICATION; Reagents; SEED; SEMENCE; SEMILLAS; TRIPSINA; TRYPSIN; Trypsin inhibitors; TRYPSINE; VIGNA RADIATA; Leguminosae; Vegetable crop; Enzyme; Proteolysis; Dicotyledones; Germination; Proteinase; Angiospermae; Vigna radiata; Spermatophyta
• ISSN: 0032-0889; 1532-2548
• DOI: 10.1104/pp.84.1.93

The proteinase (proteinase F) responsible for the initial proteolysis of the mung bean (Vigna radiata) trypsin inhibitor (MBTI) during germination has been purified 1400-fold from dry beans. The enzyme acts as an endopeptidase, cleaving the native inhibitor, MBTI-F, to produce the first modified inhibitor form, MBTI-E. The cleavage of the Asp76-Lys77 peptide bond of MBTI-F occurs at a pH optimum of 4.5, with the tetrapeptide Lys-Asp-Asp-Asp being released. Proteinase F exhibited no activity against the modified inhibitor forms MBTI-E and MBTI-C. Vicilin, the major storage protein of the mung bean, does not serve as a substrate for proteinase F between pH 4 and 7. Proteinase F is inhibited by phenylmethylsulfonyl fluoride, chymostatin, p-hydroxymercuribeanzoate, and p-chlorophenylsulfonate, but not by iodoacetate and CuCl2. It is not activated by dithiothreitol, and is stable for extended periods of time (10 months, 4°C, pH 4.0) in the absence of reducing agents. An apparent molecular weight of 65,000 was found for proteinase F by gel filtration. Subcellular fractionation in glycerol suggests that greater than 85% of the proteinase F activity is found in the protein bodies of the ungerminated mung bean. The same studies indicate that at least 56% of the MBTI of the seed is also localized in the protein bodies.