Chemical Properties
Pepsin is a white or pale yellow powder extracted from the gastric mucosa of pigs, sheep or cattle. Soluble in water, the aqueous solution is acidic. Isoelectric point pH=1. Insoluble in ethanol, chloroform, ether. It is non-toxic and has a special smell of meat; it is hygroscopic. The dry enzyme is relatively stable and will not be inactivated when heated to 1000C for 10min. Its aqueous solution is heated to above 700C or above pH6.2 and begins to inactivate, and when pH>8, it is irreversibly inactivated. It is relatively stable in strong acid solution, and the optimum pH is 1.5-2. Its digestibility is strongest when it contains 0.2% to 0.4% hydrochloric acid (pH 1.6 to 1.8), so it is often used in combination with dilute hydrochloric acid.
Definition
pepsin is an enzyme that catalysesthe breakdown of proteins topolypeptides in the vertebrate stomach.It is secreted as an inactive precursor,pepsinogen.
Preparation
Pepsin is a stomach enzyme that serves to digest proteins found in ingested food. Production method of pepsin: using porcine gastric mucosa as raw material, after extraction with phosphate buffer solution, use DEAE-cellulose column chromatography, and after acidification, use Sephadex C-25 and Sephadex G-25 column chromatography again to refine the product.
General Description
Pepsin powder is prepared from the gastric mucosa of pigs, cattle or sheep.
Biochem/physiol Actions
Unlike many other peptidases, pepsin hydrolyzes only peptide bonds, not amide or ester linkages. The cleavage specificity includes peptides with an aromatic acid on either side of the peptide bond, especially if the other residue is also an aromatic or a dicarboxylic amino acid. Increased susceptibility to hydrolysis occurs if there is a sulfur-containing amino acid close to the peptide bond, which has an aromatic amino acid. Pepsin will also preferentially cleave at the carboxyl side of phenylalanine and leucine, and to a lesser extent at the carboxyl side of glutamic acid residues. It does not cleave at valine, alanine, or glycine linkages. Z-L-tyrosyl-L-phenylalanine, Z-L-glutamyl-L-tyrosine, or Z-L-methionyl-L-tyrosine may be used as substrates for pepsin digestion. Pepsin is inhibited by several phenylalanine-containing peptides.
Purification Methods
Pepsin is re-chromatographed on a column of Amberlite CG-50 using a pH gradient prior to use. Crystallise it from EtOH. [Richmond et al. Biochim Biophys Acta 29 453 1958, Huang & Tang, J Biol Chem 244 1085 1969, 245 2189 1970.]
