Chymosin

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Chymosin ( Bos taurus )
Mass / length primary structure 323 amino acids
Isoforms A, B
Identifier
External IDs
Enzyme classification
EC, category 3.4.23.4 ,  aspartyl peptidase
MEROPS A1.006
Response type Hydrolysis of peptide bonds
Substrate Ser-Phe 105 -Met-Ala of Casein

Chymosin (also Rennin ; from ancient Greek χυμός chymos 'liquid') is an aspartate endopeptidase ( protease ). Bovine chymosin is found as a rennet enzyme in the fourth stomach ( abomasum ) of calves. Chymosin is synthesized in the form of the precursor protein PreProChymosin . This can be converted into ProChymosin , PseudoChymosin and ultimately into the active enzyme form chymosin by splitting off peptides at the amino terminal .

Precursors and activation

Chymosin is of the cells of the gastric mucosa produced in the form of the inactive precursor protein preprochymosin and as prochymosin into the lumen secreted .

In the acidic environment of the stomach , at a pH value of 4 to 5, the inactive zymogen ProChymosin is converted to the active enzyme chymosin by splitting off an amino-terminal peptide.

With very acidic chyme , below a pH value of 2.5, the cleavage takes place between amino acids 27 and 28, resulting in pseudochymosin, which is 15 amino acids longer than chymosin. Pseudochymosin can be converted to chymosin from pH 5.5.

Compared to PreProChymosin, chymosin lacks an amino-terminal sequence of 42 amino acids.

structure

The bovine protein chymosin consists of 323 amino acids with a molecular mass of 35,653  Da .

It occurs in two forms, which differ in their primary structure at amino acid position 244 ( aspartic acid or glycine ). The A-form has a slightly higher specific activity for κ- casein , but is slightly less stable than the B-form.

Function and use

The digestive enzyme chymosin is used to digest milk protein , especially casein, in the calves' digestive tract . The enzymatic cleavage process also changes the solubility of the milk protein, it is denatured and precipitated.

Chymosin is used industrially to produce cheese . It used to be obtained as a rennet from calf stomach, but it has also been genetically engineered since the 1990s . Eukaryotes such as baker's yeast or watering can mold ( Aspergillus oryzae , Aspergillus nidulans ) or Trichoderma reesei are used as genetically modified organisms (GMO) , in whose genome the cDNAs for PreProChymosin, ProChymosin and Chymosin have been transferred.

Individual evidence

  1. ↑ Renate Wahrig-Burfeind (Ed.): True. Illustrated dictionary of the German language . ADAC-Verlag, Munich 2004, ISBN 3-577-10051-6 , pp. 159 .
  2. ↑ Barkholt Pedersen, Vibeke, Kurt Asbæk Christensen, Bent Foltmann: Investigations on the activation of bovine prochymosin. In: European Journal of Biochemistry Volume 94, No. 2, 1979, pp. 573-580.
  3. ^ Daniel Cullen et al .: Controlled expression and secretion of bovine chymosin in Aspergillus nidulans. (PDF) In: Bio / Technology Volume 5, No. 4, 1987, pp. 369-376.
  4. ↑ UniProt P00794
  5. ↑ Chymosin at TransGen ( Memento of the original from April 16, 2015 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.  @1@ 2Template: Webachiv / IABot / www.transgen.de
  6. ↑ J. Mellor et al .: Efficient synthesis of enzymatically active calf chymosin in Saccharomyces cerevisiae. In: Gene Volume 24, No. 1, 1983, pp. 1-14, doi : 10.1016 / 0378-1119 (83) 90126-9 .
  7. ↑ Michael Ward et al .: Improved production of chymosin in Aspergillus by expression as a glucoamylase-chymosin fusion. In: Nature Biotechnology Vol. 8, No. 5, 1990, pp. 435-440, doi : 10.1038 / nbt0590-435 .
  8. ↑ Kozo Tsuchiya et al .: High level secretion of calf chymosin using a glucoamylase-prochymosin fusion gene in Aspergillus oryzae. In: Bioscience, Biotechnology, and Biochemistry Volume 58, No. 5, 1994, pp. 895-899, doi : 10.1271 / bbb.58.895 .
  9. ^ Daniel Cullen et al .: Controlled expression and secretion of bovine chymosin in Aspergillus nidulans. (PDF) In: Bio / technology Volume 5, No. 4, 1987, pp. 369-376.
  10. ↑ A. Harkki et al .: A novel fungal expression system: secretion of active calf chymosin from the filamentous fungus Trichoderma reesei. In: Nature Biotechnology Volume 7, No. 6, 1989, pp. 596-603, doi : 10.1038 / nbt0689-596 .