Human pepsin 3b peptide map sequence analysis, genotype and hydrophobic nature

Peptides from a Staphylococcus aureus (V8) proteinase digest of human pepsin 3b have been identified by amino acid sequence analysis. Only 137 out of 326 expected residues were detected from the C and N terminal regions of the molecule. Comparison with amino acid sequences derived from nucleotide analysis of three different pepsinogen A genes, identified 2 out of 4 possible substitutions. The presence of valine at position 30 and leucine at 291 indicates that the major pepsin component of gastric juice, pepsin 3b, corresponds to pepsinogen genotype PGA-3. Reversed-phase chromatography of native human pepsin 3b on C4 (300 A), C18 (300 A) or polymer (1000 A) columns was optimal on the C4 column and gradient elution with 2-propanol rather than acetonitrile. Denaturation of the protein in guanidinium hydrochloride, urea or high pH resulted in irreversible column retention. The marked hydrophobicity of denatured pepsin 3b may thus explain why the central segment of the protein was not revealed by peptide map analysis.