Doctor's Best Natto-Serra (Nattokinase-Serrapeptase) Is A Combination Of Two Natural Enzymes That Have Been Used As Dietary Supplements For Decades. Serrapeptase (Serratio-Peptidase) Is A Protein-Digesting Enzyme Isolated From The Friendly Bacterium Serratia E-15 Discovered In The Japanese Silkworm. Nattokinase Also Digests Protein And Is Derived From “Natto”, A Fermented Soy Food Popular In Japan For Centuries. This Nattokinase Is Free Of Vitamin K. The Serrapeptase Is Formulated With Serrateric™, A Superior Alternative To Enteric Coating That Protects The Enzyme Until It Reaches The Intestine For Optimal Absorption.