This paper by M. Kunitz, published in 1946, focuses on the properties and mechanisms of action of crystalline soybean trypsin inhibitor. The inhibitor is a globulin-type protein with a molecular weight of about 24,000 and an isoelectric point at pH 4.5. It acts as an irreversible inhibitor of trypsin by forming a stable compound with it, while it has a minor effect on chymotrypsin, forming a reversible compound. The inhibitor is non-diffusible and precipitated by trichloracetic acid. Its inhibitory action is dependent on the native state of the protein, as denaturation through heat, acid, or alkali reduces its inhibitory power. The paper also describes methods for purifying and measuring the activity of the inhibitor, including solubility tests and protein determination techniques. Additionally, it explores the digestion of the inhibitor by proteolytic enzymes and its stability under various conditions.This paper by M. Kunitz, published in 1946, focuses on the properties and mechanisms of action of crystalline soybean trypsin inhibitor. The inhibitor is a globulin-type protein with a molecular weight of about 24,000 and an isoelectric point at pH 4.5. It acts as an irreversible inhibitor of trypsin by forming a stable compound with it, while it has a minor effect on chymotrypsin, forming a reversible compound. The inhibitor is non-diffusible and precipitated by trichloracetic acid. Its inhibitory action is dependent on the native state of the protein, as denaturation through heat, acid, or alkali reduces its inhibitory power. The paper also describes methods for purifying and measuring the activity of the inhibitor, including solubility tests and protein determination techniques. Additionally, it explores the digestion of the inhibitor by proteolytic enzymes and its stability under various conditions.