A comparison of thermal characteristics and kinetic parameters of trehalases from a thermophilic and a mesophilic fungus

Abstract

Trehalases from a thermophilic fungus Thermomyces lanuginosus ( M r 145 kDa) and a mesophilic fungus Neurospora crassa ( M r 437 kDa) were purified to compare their thermal characteristics and kinetic constants. Both trehalases were maximally active at 50°C, had an acidic pH optimum and were glycoproteins (20% and 43%, w/w, carbohydrate content for T. lanuginosus and N. crassa, respectively). At their temperature optimum, their K m was similar (0.57 and 0.52 mM trehalose, for T. lanuginosus and N. crassa, respectively) but the V max of N. crassa enzyme was nine times higher than of T. lanuginosus enzyme. The catalytic efficiency, k cat / K m , for N. crassa trehalase was one order of magnitude higher (6.2×10 6 M −1 s −1) than of T. lanuginosus trehalase (4×10 5 M −1 s −1). At their T opt (50°C), trehalase from both sources exhibited similar thermostability ( t 1/2 >6 h). The energy of activation, E a , for T. lanuginosus trehalase was 15.12 kcal mol −1 and for N. crassa trehalase it was 9.62 kcal mol −1. The activation energy for thermal inactivation for the N. crassa enzyme (92 kcal mol −1) was two-fold higher than for the T. lanuginosus enzyme (46 kcal mol −1). The present study shows that the trehalase of N. crassa is not only more stable but also a better catalyst than the T. lanuginosus enzyme.