Proteases is a general term for a class of enzymes that hydrolyze protein peptide chains. According to the way they degrade polypeptides, they are divided into two categories: endopeptidases and telopeptidases. The former can cut the large molecular weight polypeptide chain from the middle to form prions and peptones with smaller molecular weights; the latter can be divided into carboxypeptidase and aminopeptidase, which respectively remove the peptide from the free carboxyl terminus or free amino terminus of the polypeptide one by one. Chain hydrolysis produces amino acids.

A general term for a class of enzymes that hydrolyze peptide bonds in proteins. According to the way they hydrolyze polypeptides, they can be divided into endopeptidases and exopeptidases. Endopeptidase cleaves the interior of the protein molecule to form smaller molecular weight peptones and peptones. Exopeptidase hydrolyzes peptide bonds one by one from the end of the free amino group or carboxyl group of protein molecules, and frees amino acids, the former is aminopeptidase and the latter is carboxypeptidase. Proteases can be classified into serine proteases, sulfhydryl proteases, metalloproteases and aspartic proteases according to their active centers and optimum pH. According to the optimum pH value of its reaction, it is divided into acidic protease, neutral protease and alkaline protease. The proteases used in industrial production are mainly endopeptidases.

Proteases are widely found in animal offal, plant stems and leaves, fruits and microorganisms. Microbial proteases are mainly produced by molds and bacteria, followed by yeast and actinomycetes.

Enzymes that catalyze the hydrolysis of proteins. There are many kinds, the important ones are pepsin, trypsin, cathepsin, papain and subtilisin. Proteases have strict selectivity for the reaction substrates they act on. A protease can only act on certain peptide bonds in protein molecules, such as the peptide bonds formed by the hydrolysis of basic amino acids catalyzed by trypsin. Proteases are widely distributed, mainly in the digestive tract of humans and animals, and are abundant in plants and microorganisms. Due to limited animal and plant resources, the industrial production of protease preparations is mainly prepared by fermentation of microorganisms such as Bacillus subtilis and Aspergillus terrestris.