based on the residues in the active site what family of proteases does pepsin belong to
Protease Proteases are used throughout an organism for various metabolic processes. Acid proteases secreted into the stomach (such as pepsin) and serine proteases present in duodenum (trypsin and chymotrypsin) enable us to digest the protein in food. Proteases present in blood serum (thrombin, plasmin, Hageman factor, etc.) play important role in blood-clotting, as well as lysis of the clots, and the correct action of the immune system. Other proteases are present in leukocytes (elastase, cathepsin G) and play several different roles in metabolic control. Some snake venoms are also proteases, such as pit viper haemotoxin and interfere with the victim's blood clotting cascade. Proteases determine the lifetime of other proteins playing important physiological role like hormones, antibodies, or other enzymes. This is one of the fastest "switching on" and "switching off" regulatory mechanisms in the physiology of an organism.
Cyclooxygenase In medicine, the root symbol "COX" is encountered more often than "PTGS". In genetics, "PTGS" is officially used for this family of genes and proteins, because the root symbol "COX" was already used for the cytochrome c oxidase family. Thus the two isozymes found in humans, PTGS1 and PTGS2, are frequently called COX-1 and COX-2 in the medical literature. The names "prostaglandin synthase (PHS)", "prostaglandin synthetase (PHS)", and "prostaglandin-endoperoxide synthetase (PES)" are older terms still sometimes used to refer to COX.