text: The enzymes trypsin and chymotrypsin were first purified in the 1930s. A serine in each of trypsin and chymotrypsin was identified as the catalytic nucleophile (by diisopropyl fluorophosphate modification) in the 1950s. The structure of chymotrypsin was solved by X-ray crystallography in the 1960s, showing the orientation of the catalytic triad in the active site. Other proteases were sequenced and aligned to reveal a family of related proteases, now called the S1 family. Simultaneously, the structures of the evolutionarily unrelated papain and subtilisin proteases were found to contain analogous triads. The charge-relay mechanism for the activation of the nucleophile by the other triad members was proposed in the late 1960s. As more protease structures were solved by X-ray crystallography in the 1970s and 80s, homologous (such as TEV protease) and analogous (such as papain) triads were found. The MEROPS classification system in the 1990s and 2000s began classing proteases into structurally related enzyme superfamilies and so acts as a database of the convergent evolution of triads in over 20 superfamilies. Understanding how chemical constraints on evolution led to the convergence of so many enzyme families on the same triad geometries has developed in the 2010s.
  Since their initial discovery, there have been increasingly detailed investigations of their exact catalytic mechanism. Of particular contention in the 1990s and 2000s was whether low-barrier hydrogen bonding contributed to catalysis, or whether ordinary hydrogen bonding is sufficient to explain the mechanism. The massive body of work on the charge-relay, covalent catalysis used by catalytic triads has led to the mechanism being the best characterised in all of biochemistry.