Serine proteases are enzyme

Enzyme

Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...

s that cleave peptide bond

Peptide bond

This article is about the peptide link found within biological molecules, such as proteins. A similar article for synthetic molecules is being created...

s in protein

Protein

Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...

s, in which serine

Serine

Serine is an amino acid with the formula HO2CCHCH2OH. It is one of the proteinogenic amino acids. By virtue of the hydroxyl group, serine is classified as a polar amino acid.-Occurrence and biosynthesis:...

 serves as the nucleophilic amino acid

Amino acid

Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...

 at the active site.
They are found ubiquitously in both eukaryotes and prokaryotes. Serine proteases fall into two broad categories based on their structure: chymotrypsin

Chymotrypsin

Chymotrypsin is a digestive enzyme that can perform proteolysis. Chymotrypsin preferentially cleaves peptide amide bonds where the carboxyl side of the amide bond is a tyrosine, tryptophan, or phenylalanine. These amino acids contain an aromatic ring in their sidechain that fits into a...

-like (trypsin-like) or subtilisin

Subtilisin

Subtilisin is a non-specific protease initially obtained from Bacillus subtilis.Subtilisins belong to subtilases, a group of serine proteases that initiate the nucleophilic attack on the peptide bond through a serine residue at the active site. They are physically and chemically...

-like.
In humans, they are responsible for co-ordinating various physiological functions, including digestion, immune response, blood coagulation and reproduction.
Chymotrypsin-like serine proteases are characterised by a distinctive structure, consisting of two beta-barrel domains that converge at the catalytic active site.