Inhibition of Serine Proteases of the Blood Coagulation System by Squash Family Protease Inhibitors

Abstract

Squash family inhibitors are the smallest protein serine protease inhibitors, being composed of approximately 30 amino acid residues. We isolated 8 squash family inhibitors from the seeds of bitter gourd, squash, gourd and luffa and examined their effect on serine proteases of the blood coagulation system. Five of them prolonged the activated partial thromboplastin time of human plasma to various extents, but three did not. Only Momordica charantia (bitter gourd) trypsin inhibitor-II prolonged the prothrombin time of human plasma. All inhibitors inhibited the amidolytic activities of factor XIIa, plasma kallikrein, factor Xa, but did not inhibit significantly those of factor XIa, factor IXa, factor VIIa, and thrombin. Ki values for factor XIIa, plasma kallikrein, and factor Xa were in the order of 10(-6)-10(-9), 10(-4)-10(-5), and 10(-4)-10(-6)M, respectively. The prolongation of the activated partial thromboplastin time by inhibitors appeared to correspond to their inhibitory potencies for factor XIIa. Momordica charantia trypsin inhibitor-II, which has the strongest inhibitory potency toward the amidolytic activity of factor Xa, with a Ki value 10-100 times smaller than those of other inhibitors, inhibited the activation of factor X by factor VIIa-tissue factor complex or factor IXa, while others did not.

Proteinase inhibitors and their function in plants: A review

“…The overwhelming majority of the proteins found in Cucurbitaceae are potent trypsin inhibitors (K i ranges from 0.001 to 0.01 nM), which is in complete correspondence with the structure of their active sites [30]. Some of the representatives of the family are capable of affecting other enzymes with trypsin specificity; the latter include enzymes from blood plasma, such as activated Hagemann factor, callicrein, plasmin, and thrombin [159][160][161]. The inhibitors from balsam pear are an exception in this case, as well, since they are efficient in suppressing the activity of elastase [162].…”

Pharmacological actions and potential uses of Momordica charantia: a review

“…Wang and Ng (2001b) observed mild hypotensive response with Momordin. In another study, MC prolonged prothrombin time by inhibiting activation of factor X by factor VIIa-tissue factor complex or factor IXa, (Hayashi et al, 1994).…”

NMR studies of internal dynamics of serine proteinase protein inhibitors: Binding region mobilities of intact and reactive‐site hydrolyzed Cucurbita maxima trypsin inhibitor (CMTI)‐III of the squash family and comparison with those of counterparts of CMTI‐V of the potato I family

“…1B). Natural and chemical variants of the squash inhibitor have been demonstrated to inhibit physiologically important serine proteinases, such as factor XIIa (Hojima et al, 1982;Krishnamoorthi et al, 1990;Wynn & Laskowski, 1990;Hayashi et al, 1994), cathepsin G (McWherter et al, 1989, and plasmin (Otlewski et al, 1990). Solution NMR studies of CMTI-III* and CMTI-I*, as well as the thermodynamics of the trypsin-catalyzed equilibrium, CMTI-111 * CMTI-III*, have been reported (Krishnamoorthi et al, 1992a(Krishnamoorthi et al, , 1992b.…”