| Comments |
P.214 bottom paragraph: "Another parameter which can play an important role in chemical reactions controlled by enzymes is the Km. On a first approximation, this represents the affinity of the enzyme for the substrate, provided that the rate constants that could interfere with the constants directly involved in the true dissociation constant of the enzyme-substrate complex can be neglected. Km values have been reported for numerous cold-adapted enzymes and compared to those of mesophilic homologues (Table 10.1). With the exception of the lactate dehydrogenases, this table reveals a main feature of cold-adapted enzymes, i.e. their Km values are higher than that of their mesophilic homologues, indicating a lower affinity for the substrate. Indeed, this loss in substrate binding affinity contributes to fix the limit of the thermal tolerance of living organisms. The increase of Km in cold-adapted enzymes suggests that the active sites of these have lost part of their initial rigidity and that the enzyme-substrate complex ES is less stable than in mesophilic and a fortiori thermophilic counterparts." |