The reactions between laccase and different substrates (3, 4-dihydroxybenzaldehyde, guaiacol, pyrogallol, gallic acid) have been studied by LKB-2107 batch microcalorimetry system. The Michaelis constant (Km), the rate constant (k2) and thermodynamic parameters (ΔrHm, ΔG0, ΔT^≠, Ea, ΔST^≠) have been determined. The process of the reactions have been analyzed by using the transition state theory. The results show that formation of an enzyme-substrate complex is "anticatalytic". The entire and sole source of catalytic power is the stabilization of transition state; reactant-state interactions are by nature inhibitory and only waste catalytic power. The activation entropy (ΔST^≠ <0) indicated that enzyme-transition structure is bound more tightly than enzyme-substrate complex.

Key words: BENZALDEHYDE P, REACTION KINETICS, BENZENECARBOXYLIC ACID P, CALORIMETRY, TRANSITION STATE THEORY, BENZENETRIOL, THERMOGRAPHY, PHENAL P, LACCASE