Cod (Gadus morhua) trypsin heat inactivation: A reaction kinetics study

The heat inactivation of cod (Gadus morhua) trypsin was examined at 40-55C by nonlinear regression (NLR) analysis according to 1st-order, n-th order, or consecutive reaction kinetics. At 40C Cod trypsin was inactivated by a 2nd-order reaction; n = 2 (+/-0.014) with a pseudo rate constant (k') of 6.46 (+/-0.04) x 10(-4) (s(-1)). The order of reaction decreased with increasing temperature; n = 1.54 (+/-0.003) at 45C, n = 0.8 (+/-0.005) at 50C or n = 0.64 (+/-0.014) at 55C. At 45-55C the consecutive model also indicated Ist-order inactivation kinetics. SDS-PAGE analysis showed that with progressive heating the concentration of cod trypsin decreased and there was an appearance of lower molecular weight polypeptides. The results are consistent with a heat inactivation process involving trypsin autolysis. A mechanism for cod trypsin heat inactivation is proposed which accounts for the observed 1st-order or 2nd-order reaction kinetics as limiting cases.