Pepsin A

{{Infobox enzyme

| Name = Pepsin A

| EC_number = 3.4.23.1

| CAS_number = 9001-75-6

| GO_code =

| image = 1pso.jpg

| width = 270

| caption = Pepsin + inhibitor (l.blue), Human

}}

Pepsin A ({{EC number|3.4.23.1}}, pepsin, lactated pepsin, pepsin fortior, fundus-pepsin, elixir lactate of pepsin, P I, lactated pepsin elixir, P II, pepsin R, pepsin D) is an enzyme.{{cite journal | vauthors = Lee D, Ryle AP | title = Pepsinogen D. A fourth proteolytic zymogen from pig gastric mucosa | journal = The Biochemical Journal | volume = 104 | issue = 3 | pages = 735–41 | date = September 1967 | pmid = 4167464 | pmc = 1271213 }}{{cite journal | vauthors = Lee D, Ryle AP | title = Pepsin D. A minor component of commercial pepsin preparations | journal = The Biochemical Journal | volume = 104 | issue = 3 | pages = 742–8 | date = September 1967 | pmid = 4860638 | pmc = 1271214 }}{{cite journal | vauthors = Foltmann B | title = Gastric proteinases--structure, function, evolution and mechanism of action | journal = Essays in Biochemistry | volume = 17 | pages = 52–84 | date = 1981 | pmid = 6795036 }}{{cite journal | vauthors = James MN, Sielecki AR | title = Molecular structure of an aspartic proteinase zymogen, porcine pepsinogen, at 1.8 A resolution | journal = Nature | volume = 319 | issue = 6048 | pages = 33–8 | date = 1986 | pmid = 3941737 | doi = 10.1038/319033a0 }}{{cite book | chapter = Aspartyl proteinases | title = New Comprehensive Biochemistry: Hydrolytic Enzymes |author1 = Fruton, J.S. |date = 1987 |volume = 16 |pages = 1–38 |editor = Neuberger, A. |author2 =Brocklehurst, K. |publisher = Elsevier |location = Amsterdam }}{{cite journal | vauthors = Tang J, Wong RN | title = Evolution in the structure and function of aspartic proteases | journal = Journal of Cellular Biochemistry | volume = 33 | issue = 1 | pages = 53–63 | date = January 1987 | pmid = 3546346 | doi = 10.1002/jcb.240330106 }}{{cite journal | vauthors = Pohl J, Dunn BM | title = Secondary enzyme-substrate interactions: kinetic evidence for ionic interactions between substrate side chains and the pepsin active site | journal = Biochemistry | volume = 27 | issue = 13 | pages = 4827–34 | date = June 1988 | pmid = 3139029 | doi = 10.1021/bi00413a037 }} This enzyme catalyses the following chemical reaction

: Preferential cleavage: hydrophobic, preferably aromatic, residues in P1 and P1' positions. Cleaves Phe¹-Val, Gln⁴-His, Glu¹³-Ala, Ala¹⁴-Leu, Leu¹⁵-Tyr, Tyr¹⁶-Leu, Gly²³-Phe, Phe²⁴-Phe and Phe²⁵-Tyr bonds in the B chain of insulin

The enzyme is a predominant endopeptidase in the gastric juice of vertebrates.