Nomenclature
CAS number: 9001-98-3
Chymosin; rennase; lab; abomasal enzyme; Lab Ferment (German).
Description and references
Mol wt about 31,000. The predominant milk-clotting
enzyme from the true stomach or abomasum of the suckling calf: Tauber,
Kleiner, J. Biol. Chem. 96, 745 (1932). Secreted as an inactive precursor called prorennin and converted in the acid environment of the stomach to
the active enzyme. Obtained by extracting dried strips of calf stomach
with 5 to 10% NaCl soln contg boric acid for 5 days; improved process:
Keil, US 2339931 (1942). Structure consists
of a single polypeptide chain with internal disulfide bridges. Amino
acid composition: Schwander et al., Helv. Chim. Acta 35, 553 (1952). Determn
of N-terminal amino acid sequence: Foltmann, Philos. Trans. R. Soc. London 257B, 147 (1970). Homologies in amino acid sequences of rennin and pepsin:
Tang, Hartley, Biochem. J. 118, 611 (1970). Reviews: Berridge, Adv. Enzymol. 15, 423 (1954);
Foltmann, Milk Proteins 2, 217 (1971).
Properties
Yellowish powder, grains or scales. Peculiar,
not unpleasant odor. Characteristic, slightly salty taste. Slightly
hygroscopic. Can be purified enough to crystallize. The dry substance
(sometimes diluted with NaCl or lactose) is stable, aq solns are not.
Partially sol in water, dil alcohol. Insol at pH values near its
isoelectric point of pH 4.5. pH of aq soln 5.8 (acceptable range
5.3-6.3). Strongly affected by ultraviolet (sunlight). Causes milk
to coagulate, optimum temp 37-43°, optimum pH of milk 5.8. Not active
below 15° nor above 55°. When a commercial prepn is labeled 1:10,000
it means that one gram will curdle 10 liters of milk at 35° within
40 minutes. Other strengths are 1:100,000 to 1:7,600,000.Use
Rennet (a dried extract contg rennin) is used in the manuf of
cheese and rennet casein, also sold retail for the making of junket
or rennet custards.
Therapeutic Category
Digestive enzyme.
Keywords
Digestive Aid; Enzyme; Digestive