THERMAL-STABILITY OF IMMOBILIZED ALPHA-CHYMOTRYPSIN IS ADDITIONALLY INCREASED BY CHAOTROPIC COMPOUNDS

Temperature dependence of the rate constant of irreversible thermal in activation, k(in), of immobilized alpha-chymotrypsin depends markedly on the number of covalent bonds between the enzyme and support. When t he number of bonds is big enough (thirteen), the dependence is linear as presented in Arrhenius plot (log k(in) versus reciprocal temperatur e). However, if the number of such bonds is moderate or;small (six or two), the temperature dependence of k(in) has a pronounced 'zig-zag' c haracter. This difference in the inactivation behaviour is attributed to an ability of 'moderately or mildly' attached alpha-chymotrypsins t o accomplish a transition into a less ordered, catalytically inactive conformation and to inability of 'rigidly' bound enzyme to pass such a transition. Chaotropic salts additionally stabilize this loose confor mation of 'mildly or moderately' bound alpha-chymotrypsins against irr eversible thermal inactivation but are without effect on the stability of 'rigidly' bound enzyme.