Source: Porcine Stomach
Pepsin is an acidic protease. Its inactive zymogen precursor, pepsinogen, is produced in the stomach mucosa. There are several pepsins designated A, B, C, and D. Pepsin A, the major component, has a molecular weight of 35,000 daltons and an optimum pH of approximately 1.0 for substrates such as casein or hemoglobin if the substrate is native protein. Pepsin cleaves proteins preferentially at carboxylic groups of aromatic amino acids such as phenylalanine and tyrosine. It will not cleave at bonds containing valine, alanine or glycine. Pepsin is assayed based on the method of Anson J. Gen. Physiol., 22, 79 (1938) using hemoglobin as the substrate. Pepsin is unstable above pH 6.
Stability/Storage: Pepsin for 1-2 years at 2-8°C.
Unit Definition: One Unit releases 0.001 A280 as TCA soluble hydrolysis products from denatured hemoglobin per minute at 37°C. One FIP Unit, expressed as micromoles of tyrosine equivalents liberated per minute at 25°C, can be calculated as follows: 1 Worthington Unit x 0.0071 = FIP units.