Protease hydrolyzing casein

Fiq. 4. Hydrolysis of casein by several proteinases. I. Hydrolysis of casein by trypsin (A), chymotrypsin (Q), or subtilisin ( ) followed by S. griseus protease (O)- Curves B, C, and D indicate the extent of hydrolysis by individual enzymes without addition of S. griseus protease. Curve A indicates the extent of hydrolysis when S. griseus protease is added to the hydrolyzate of one of the other proteinases after approximately 47 hr. II. Hydrolysis of casein by S. griseus protease followed by hydrolysis with trypsin, chymotrypsin, subtilisin, or pepsin. The latter enzymes were added to the protease hydrolyzate after approximately 47 hr. From Nomoto et al. (1960a,b). 

Enzymes can be coupled to the surface of a very open-pored silica gel to obtain a relatively stable fixed enzymatic catalyst (282). Porous silica with a pore diameter of 51 nm was used as a carrier to the surface of which the enzyme B. subtilic protease was attached, a bifunctional diazonium salt-was reacted with the surface of the silica, followed by reaction of enzyme with the other end of the diazonium molecule. The silica-supported enzyme hydrolyzed casein and had a half-life of more than 7 months whereas that of enzyme simply adsorbed on the silica was 2.5 months. 

This enzyme [EC 3.4.21.53], also known as endopepti-dase La, ATP-dependent serine proteinase, and ATP-dependent protease La, catalyzes the hydrolysis of peptide bonds in large proteins (for example, globin, casein, and denaturated serum albumin) in the presence of ATP (which is hydrolyzed to ADP and orthophosphate). Vanadate ion inhibits both reactions. A similar enzyme occurs in animal mitochondria. Protease La belongs to the peptidase family S16. 

The other major casein in cheese is /3-casein, but it is generally not hydrolyzed by rennet in low-pH cheeses. Alkaline milk protease (plas-min) plays the major role in the hydrolysis of /3-casein (Richardson and Pearce 1981). The plasmin level in cheese is related to the pH of the curd at whey drainage, since plasmin dissociates from casein micelles as the pH is decreased. Richardson and Pearce (1981) found two or three times more plasmin activity in Swiss cheese than in Cheddar cheese. Swiss cheese curds are drained at pH 6.4 or higher, while Cheddar cheese curds are drained at pH 6.3 or lower. Proteolysis of /3-casein is significantly inhibited by 5% sodium chloride. The inhibitory influence of sodium chloride is most likely due to alteration of /3-casein or a reduction in the attractive forces between enzyme and substrate (Fox and Walley 1971). 

Actinidin also hydrolyzes a-casein and (3-casein in milk (Nishiyama and Oota, 2002 Yamaguchi et al, 1982). Bachmann and Farah (1982) demonstrated the occurrence of a bitter taste in mixtures of milk proteins and raw kiwifruit, which was attributed to a caseinolytic protease in kiwifruit splitting casein into bitter peptides. 

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