Thermochimica Acta, Vol.303, No.2, 191-196, 1997
Studies on single-substrate, enzyme-catalyzed reactions and analysis of transition state by microcalorimetry
The reactions between Laccase and various substrates (3,4-Dihydroxybenzaldehyde, Guaiacol, Pyrogallol, Gallic acid) have been studied using LKB-2107 batch microcalorimetry system. Thermodynamic parameters (Delta(r)H(m), Delta G(0), Delta G(T)(not equal) E-a, Delta S-T(not equal)) and kinetic parameters (K-m,k(2)) have been calculated. The reactions process have been analyzed from free energy changes by using the transition state theory which showed that formation of an enzyme-substrate complex is 'anticatalytic.' The experimental results also indicated that stabilization of enzyme-substrate complex slows down the reaction, whereas stabilization of transition state accelerates it. Two methods are proposed to enhance catalytic power of Laccase. The decrease of activation entropy (Delta S-T(not equal) < 0) indicated that enzyme-substrate/transition structure is more tightly bound than enzyme-substrate complex structure.