Pepsíns

Pepsins are a group of proteolytic enzymes that initiate the digestion of proteins in the stomach. They belong to the aspartic protease family and are produced by the gastric mucosa of many vertebrates, including humans. The family includes several members, commonly referred to as pepsin A, pepsin B, and related enzymes, which share a conserved catalytic mechanism.

Pepsins are synthesized as inactive zymogens, pepsinogens A and B, by chief cells in the gastric mucosa. In the acidic environment of the stomach (pH around 1.5–2.5), pepsinogen undergoes autocatalytic activation to pepsin, an active aspartic protease that operates best at low pH. The active site uses two aspartic acid residues to hydrolyze peptide bonds.

Pepsin cleaves preferentially on the carboxyl side of hydrophobic and aromatic residues, notably phenylalanine, leucine, tyrosine, and tryptophan, producing smaller polypeptides that are further digested by pancreatic enzymes in the small intestine.

By initiating protein digestion in the stomach, pepsins facilitate subsequent proteolysis and nutrient absorption. Their activity is limited to acidic environments and diminishes as the gastric pH rises.

Regulation and variants: Pepsin activity is inhibited by natural inhibitors such as pepstatin. In many mammals there are multiple pepsin genes and enzymes (e.g., pepsin A, B), with slightly different substrate preferences and pH optima.

Clinical and research notes: Impairment of pepsin production or function can affect protein digestion. Pepsins are also used in experimental studies of protein structure and digestion under acidic conditions.