Milk-clotting mechanism of Dregea sinensis Hemsl. protease.
Dregea sinensis Hemsl. is used as a milk coagulant to produce goat milk cakes in Yunnan, China. However, the composition of milk-clotting compounds and the related mechanism have not been reported. Crude protease was extracted from the stem, purified, and then separated with a Millipore ultrafiltration centrifuge tube. Cysteine protease (procerain B) was identified as the main milk-clotting protein through electrospray ionization mass spectrometry, and its molecular weight was 23.8 kDa. The protease can partially degrade α-casein (CN) and completely degrade β- and κ-CN, and κ-CN degradation resulted in milk clotting. The molecular weight and AA sequence of the peptide fractions were determined through matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and a peptide sequencer, respectively. The enzyme cleaved κ-CN at Ala90-Gln91 and produced deputy κ-CN and caseinomacropeptide with molecular weights of 12 and 6.9 kDa, respectively. This cleavage site differed from the majority of chymosins cleaved at Phe105-Met106.
College of Food Science and Technology, Yunnan Agricultural University, Kunming 650201, Yunnan, China.
Yali
Y
Zhang
College of Food Science and Technology, Yunnan Agricultural University, Kunming 650201, Yunnan, China.
Hongyan
H
Wang
College of Food Science and Technology, Yunnan Agricultural University, Kunming 650201, Yunnan, China.
Liang
L
Tao
College of Food Science and Technology, Yunnan Agricultural University, Kunming 650201, Yunnan, China. Electronic address: aixianghuang@126.com.
Ai-xiang
AX
Huang
D000818:Animals; D029062:Apocynaceae / Q000201:enzymology*; D002364:Caseins / Q000378:metabolism; D002681:China; D057056:Cysteine Proteases / Q000378:metabolism*; D010450:Endopeptidases / Q000378:metabolism; D008892:Milk / Q000737:chemistry*; D008894:Milk Proteins / Q000032:analysis / Q000378:metabolism*; D008970:Molecular Weight; D010446:Peptide Fragments / Q000378:metabolism; D021241:Spectrometry, Mass, Electrospray Ionization
D002364:Caseins; D008894:Milk Proteins; D010446:Peptide Fragments; C065989:caseinomacropeptide; D057056:Cysteine Proteases; D010450:Endopeptidases
Dregea sinensis Hemsl. protease; enzyme cleavage site; separation and identification; κ-casein