Studies on single-substrate, enzyme-catalyzed reactions and analysis of transition state by microcalorimetry

• Published in: Thermochimica acta Vol. 303; no. 2; pp. 191 - 196
• Main Authors: Wang, Tianzhi, Liu, Yi, Li, Weiping, Wan, Hongwen, Yang, Feng, Wu, Dingquan, Qu, Songsheng
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 30.10.1997; Elsevier Science
• Subjects: Analytical, structural and metabolic biochemistry; Biological and medical sciences; Enzymes and enzyme inhibitors; Fundamental and applied biological sciences. Psychology; Laccase; Microcalorimetry; Oxidoreductases; Substrate; Thermokinetics; Transition state; Substrate; Microcalorimetry; Thermokinetics; Transition state; Laccase; Gibbs free energy; Enzyme; Entropy; Substrate enzyme complex; Binding energy; Thermodynamic parameter; Oxidoreductases; Kinetic parameter; Catalyst activity; Activation energy
• ISSN: 0040-6031; 1872-762X
• DOI: 10.1016/S0040-6031(97)00249-9

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 ( Δ r H m, ΔG 0, ΔG ≠ T, E a, ΔS ≠ T) 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 ( ΔS ≠ T < 0) indicated that enzyme-substrate/transition structure is more tightly bound than enzyme-substrate complex structure.