Cysteine protease activity in bovine milk
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- 作者：Magboul ; Abdallah A.A. ; Larsen ; Lotte B. ; McSweeney ; Paul L.H. ; Kelly ; Alan L.
- 关键词：Cysteine protease ; Cathepsin B ; Milk ; Proteolysis
- 刊名：International Dairy Journal
- 出版年：2001
- 出版时间：2001
- 年：2001
- 卷：11
- 期：11-12
- 页码：865-872
- 全文大小：241 K
文摘
Proteolytic activity of native cysteine proteases was studied in bovine milk. Five fractions (fI–fV) with cysteine protease activity were separated from acid whey prepared from raw bovine milk by ion-exchange chromatography on Q-Sepharose. The hydrolytic action of the most active fractions (fIII and fV), after further purification using gel permeation chromatography on Superdex S75, was studied against individual caseins. The two fractions contained different cysteine protease activities capable of hydrolyzing both 45;s1- and 46;-casein. Studies of the effects of different reagents on the activity of partially purified fIII showed that the activity in this fraction was unaffected by aprotinin, slightly inhibited by p-chloromercuribenzoate and o-phenanthroline and completely inhibited by l-trans-epoxysuccinyl-l-leucylamido (4-guanidino) butane, consistent with identification as a cysteine protease. Phenylmethylsulphonyl fluoride and pepstatin A reduced activity of fIII by 40 % and 50 % , respectively. The partially purified fIII retained 
20 % of its cysteine protease activity after heating at 55°C, 60°C, 65°C and 72°C for 40min, 20min, 10min and 30s, respectively. Immunoblotting of fIII with antibodies to the bovine lysosomal cysteine protease, cathepsin B, clearly indicated the presence of immunoreactive cathepsin B in this fraction. This study presents strong evidence for the presence of a heterogeneous group of cysteine proteases in bovine milk, with one of these enzymes probably being cathepsin B.
20 % of its cysteine protease activity after heating at 55°C, 60°C, 65°C and 72°C for 40min, 20min, 10min and 30s, respectively. Immunoblotting of fIII with antibodies to the bovine lysosomal cysteine protease, cathepsin B, clearly indicated the presence of immunoreactive cathepsin B in this fraction. This study presents strong evidence for the presence of a heterogeneous group of cysteine proteases in bovine milk, with one of these enzymes probably being cathepsin B.