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Chymosin, or rennin, is an enzyme of the hydrolase class (and of the A1 peptidase family), necessary for the digestion of casein present in milk.
Chymosin is produced, together with pepsinogen, by adelomorphic (or zymogenic) cells at the level of the gastric glands of the stomach mucosa.
The production of this enzyme is greater in the neonatal period. The specificity of the enzyme is very broad and overlaps with that of pepsin A. The preferential cleavage is at the Ser-Phe105┼Met-Ala site of the κ chain of casein.
Chymosin is, therefore, an enzyme that plays a fundamental role in the milk coagulation process during cheese production.
Chymosin is responsible for the protein coagulation of milk, a crucial step in cheese production. Essentially, it acts on the casein present in milk, causing the formation of a gelatinous structure known as rennet.
Chymosin is used, therefore, to cause extensive precipitation and curd formation in cheese production. The native substrate of chymosin is K-casein which is specifically cleaved in the peptide bond between amino acid residues 105 and 106, phenylalanine and methionine. The product obtained is calcium phosphocaseinate. When the specific bond between the hydrophobic (para-casein) and hydrophilic (acid glycopeptide) groups of casein is broken, the hydrophobic groups come together and form a 3D network that traps the aqueous phase of the milk.
Charge interactions between the histidines on kappa-casein and the glutamates and aspartates of chymosin initiate binding of the enzyme to the substrate. When chymosin does not bind the substrate, a beta hairpin, sometimes called “the flap”, can hydrogen bond with the active site, covering it and preventing further binding of the substrate.
Chymosin can be produced from several sources, including microbial organisms, animals, and genetic engineering. Traditionally, it was mainly extracted from the stomachs of young ruminants such as calves and goats, but is now often produced through bacterial fermentation or genetic engineering.
Chymosin is a proteolytic enzyme, meaning it is able to cleave protein bonds in casein molecules found in milk. This splitting process is what leads to milk coagulation.
This enzyme works best at moderate temperatures (around 30-40°C) and in a slightly acidic environment (pH between 5.0 and 6.5), conditions typically found in the cheese-making process.
Chymosin is highly specific for casein, meaning it has a strong affinity for this protein substrate and does not act on other proteins present in milk.
Furthermore, due to its ability to coagulate milk, chymosin is a key ingredient in the production of various types of cheeses, contributing to their texture and structure.
In addition to the food sector, chymosin has found use in several biotechnological applications, including the production of recombinant proteins for therapeutic and industrial uses.

Warning: The information provided is not medical advice and may not be accurate. The contents are for illustrative purposes only and do not replace medical advice.

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