INHIBITORY SPECIFICITY AGAINST VARIOUS TRYPSINS AND STABILITY OF OVOMUCOID FROM JAPANESE-QUAIL EGG-WHITE

The inhibitory specificity and stability of ovomucoid from Japanese qu ail egg white (OMJPQ) were examined to understand its nutritional sign ificance. OMJPQ showed strong inhibitory activities toward trypsins fr om various origins including human, and the trypsin inhibitions occurr ed at molar ratios of enzyme to inhibitor between 1/1 and 2/1. On the other hand, an equimolar mixture of the second and third domains of OM JPQ inhibited bovine trypsin more strongly than the corresponding nati ve OMJPQ did. This distinction was partly explained by the presence of steric hindrance on the formation of a 2:1 trypsin-OMJPQ complex. OMJ PQ retained about 100% of its original activity over a pH range from 1 to 12 after a 24-h incubation at 37 degrees C. The inhibitor was most thermostable between pH 2 and 5, where more than 70% of its original activity was maintained after a l-h incubation at 100 degrees C and ab out 25% of the activity even after a 30-min incubation at 121 degrees C. OMJPQ was also considerably resistant to pepsin attack. Pepsin dige stion of the protein resulted in only about 40% loss of the original t rypsin-inhibitory activity even after a 24-h digestion. Furthermore, t he addition of bovine serum albumin to the digestion mixture brought a bout rapid elevation in the trypsin-inhibitory activity during an init ial 30-min digestion. SDS-PAGE and immunoblot suggested that this was due to the liberation of active inhibitory domains from the native mol ecule by inter-domain proteolysis.