Inhibition of bovine trypsin by the phosphorylated N-terminal part beta(1-105) of beta-casein.
The sensitivities of the R25-I26 bond on bovine beta-casein and on its N-terminal fragment beta(1-105) to trypsin digestion were compared by monitoring the liberation of the beta(1-25) product. It was shown that this peptide bond was poorly and slowly hydrolysed on beta(1-105), while it is highly susceptible to trypsin attack when whole protein is used as substrate. The marked resistance of beta(1-105) is linked to its inhibitory effect on trypsin activity (apparent K'i = 1.2 x 10(-6) M), as demonstrated by using a related chromogenic substrate. Indeed, a preincubation step of trypsin with beta(1-105) leads to a more pronounced inhibitory effect. The progress curves obtained with and without preincubation show that beta(1-105) acts as a slow binding inhibitor on trypsin activity. These findings promise further insight into the action and the regulation of proteolytic enzymes.
Bouhallab
S
S
INRA, Laboratory For Research in Dairy Technology, Rennes, France.
Sapin
B
B
Mollé
D
D
Henry
G
G
Léonil
J
J
D000595:Amino Acid Sequence; D000818:Animals; D002364:Caseins / Q000494:pharmacology*; D002417:Cattle; D006868:Hydrolysis; D007700:Kinetics; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000494:pharmacology*; D010766:Phosphorylation; D017386:Sequence Homology, Amino Acid; D014361:Trypsin Inhibitors / Q000494:pharmacology*
D002364:Caseins; D010446:Peptide Fragments; D014361:Trypsin Inhibitors; C106659:beta-casein (1-105)