Characterization of human pepsin I obtained from purified gastric pepsinogen I

Immunochemical homogeneous human pepsinogen I-group (PgI) was purified by solid immunoadsorbent and by DEAE-chromatography from gastric mucosa. PgI contained five electrophoretic distinct bands at pH 8.2 but only four bands at pH 5.6. After acid activation human pepsin (PI) was separated from the inhibitory peptide by affinity chromatography using poly-L-lysine. Purified PgI contained 9-16% of the inhibitory peptide. The yield of PI was 64 to 85%. A 65% increase of specific activity was observed. PI demonstrated three bands in agar gel electrophoresis at pH 5.6. The pH range of PI was rather wide, showing two maxima at pH 2.0 and pH 3.0 with hemoglobin as substrate. Irreverisble inactivation of PI was observed at pH 7.0 and at a temperature of 60 degrees C. The Km-value of PI was 0.170 mmol as determined with N-acetyl-L-phenyl-alanyl-L-3,5 diiodotyrosine. The specific activity was 9.6 IU/mg (hemoglobin substrate) and 0.032 IU/mg (dipeptide substrate). Porc pepsinogen (PPg) and its activated pepsin (PP) was used for comparison. PP showed indentical elution patterns in affinity chromatography. In AEE PPg and PP demonstrated both two components at pH 5.6 with different electrophoretic mobilities. The pH optimum of PP was observed at pH 2.0. PP was slightly more sensitive in alkali and heat inactivation than human P. A higher Km-value of PP of 0.082 mmol and higher specific activity as compared to human PI was observed.