Molecular Weight and Amino Acid Composition of Human Gastricsin and Pepsin

Abstract

Abstract Molecular weights for human pepsin and gastricsin are about 34,000 and 31,500, respectively, as determined by the sedimentation-diffusion method, sedimentation equilibrium studies, and amino acid analysis data. The sedimentation coefficients, s20,w, were found to be 3.14 S for human pepsin and 3.32 S for gastricsin. The sedimentation coefficient for gastricsin is concentration-dependent. The diffusion coefficients, D20,w, were found to be 8.7 x 10-7 cm2 sec-1 and 9.6 x 10-7 cm2 sec-1 for human pepsin and gastricsin, respectively. The partial specific volumes calculated from the amino acid compositions were 0.724 ml per g for human pepsin and 0.724 ml per g for gastricsin. The amino acid composition of human pepsin is very similar to that of procine pepsin. Human pepsin contains a significantly higher number of aspartic acid, isoleucine, and serine residues than gastricsin, while gastricsin contains a significantly higher number of glutamic acid residues.