Molecular Weight and Amino Acid Composition of Human Gastricsin and Pepsin

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.