Unsaturated fatty acids enhance the fibrinolytic activity of subtilisin NAT (nattokinase)

Subtilisin NAT (STN), alternatively designated nattokinase, is a serine protease with potent fibrinolytic activity. In this study, we screened several foods to enhance the fibrinolytic potential of STN and identified unsaturated fatty acid-rich ones as candidates. We isolated linoleic acid as a major active compound from one of the most active foods, red pepper. Linoleic acid promoted the STN-mediated fibrin/fibrinogen degradation at >20 μg/ml. STN cleaved three of the fibrinogen polypeptide chains, among which linoleic acid accelerated Bβ-chain and γ-chain degradations, but slightly suppressed the degradation of α-chain fragments. Linoleic acid failed to affect small synthetic peptide degradation, suggesting a conformational modulation of fibrin/fibrinogen for the linoleic acid promotion of STN activity. Of the various fatty acids tested, unsaturated ones were active but saturated ones were rather inhibitory to STN-mediated fibrinolysis. Thus, our data shed new light on the dietary promotion of STN activity. Practical applications Subtilisin NAT (STN) is a serine protease abundantly contained in natto, a soybean food fermented with Bacillus subtilis var. natto. The use of STN as functional foods to improve blood circulation is getting attention because STN actively degrades fibrin. Our results demonstrate that widely occurring unsaturated fatty acids such as linoleic, eicosapentaenoic, and docosahexaenoic acids enhance the fibrinolytic activity of STN. Thus, the intake of natto or STN supplements in combination with unsaturated fatty acid-containing oil can be a novel way to gain cardiovascular benefits.