Primate pepsins : evolution, function, and adaptation to feeding strategy

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Pepsins are gastric digestive proteinases in vertebrates, including man. There are five forms, i.e., pepsins A, B, and F, gastricsin, and chymosin, which have evolved from a common ancestral aspartic proteinase. The specificity is well explained with the very hydrophobic nature of the S1' subsite, consisting of Tyr^<189>, Ile^<213>, Ile^<300>, Met^<289>, Val/Leu^<291>, and Leu^<298>. The first three residues are well conserved in pepsin family enzymes. Fourteen different pepsinogen-A cDNAs and one pepsinogen-C cDNA have been cloned from gastric mucosa of the orangutan, Pongo pygmaeus. The extreme multiplication in the orangutan might be advantageous for the digestion of herbaceous foods due to the increase in the level of enzymes in stomach and the diversification of enzyme specificity.