Nattokinase NSK-SDIsolated, purified and encapsulated nattokinase, an enzyme derived from boiled soybeans and a selected, patented strain of Bacillus subtilis natto. Nattokinase NSK SD was the first nattokinase introduced into the US market, and it has established standardization and quality levels for all nattokinase, with comprehensive safety studies and proven potency. It is vegetarian, non irradiated, and free of vitamin K2. NSK SD has two Japanese and three U. S.