Enzyme kinetics II

The catalytic properties of enzymes, and consequently their activity (see p. 90), are influenced by numerous factors, which all have to be optimized and controlled if activity measurements are to be carried out in a useful and reproducible fashion. These factors include physical quantities (temperature, pressure), the chemical properties of the solution (pH value, ionic strength), and the concentrations of the relevant substrates, cofactors, and inhibitors. 

The effect of enzymes is strongly dependent on the pH value (see p.30). When the activity is plotted against pH, a bell-shaped curve is usually obtained (1). With animal enzymes, the pH optimum—i.e., the pH value at which enzyme activity is at its maximum—is often close to the pH value of the cells (i.e., pH 7). 

The temperature dependency of enzymatic activity is usually asymmetric. With increasing temperature, the increased thermal movement of the molecules initially leads to a rate acceleration (see p.22). At a certain temperature, the enzyme then becomes unstable, and its activity is lost within a narrow temperature difference as a result of denatu-ration (see p. 74). The optimal temperatures of the enzymes in higher organisms rarely exceed 50 °C, while enzymes from thermophilic bacteria found in hot springs, for instance, may still be active at 100 °C. 

Koolman, Color Atlas of Biochemistry, 2nd edition 2005 Thieme 

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Bloomfield, V., Peller, L., Alberty, R. A. (1962a). Multiple intermediates in steady-state enzyme kinetics II. Systems involving two reactants and two products. J. Amer. Chem. Soc. 84, 4367-4374. 

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