Serrapeptase is a proteolytic enzyme isolated from the nonpathogenic bacteria serratia species found in the digestive tract of the japanese silkworm. serrapeptase has been used as a nutritional supplement in europe and asia for nearly three decades. each enteric-coated vegetarian capsule of best serrapeptase contains pure serrapeptase designed for optimal absorption in the intestinal tract.note: doctor's best serrapeptase contains 40,000 serratiopeptidase units, which refers to the enzyme activity level. enzymes, like serrapeptase, are not measured in mg, but in an unassociated measure of units.doctor's best serrapeptase has 40,000 serratiopeptidase (units) of activity per capsule. this is a very high amount of activity.