A comparison of thermal characteristics and kinetic parameters of trehalases from a thermophilic and a mesophilic fungus.
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 degrees 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 x 10(6) M(-1) s(-1)) than of T. lanuginosus trehalase (4 x 10(5) M(-1) s(-1)). At their T(opt) (50 degrees 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.
Bharadwaj
G
G
Department of Biochemistry, Indian Institute of Science, Bangalore, India.
Maheshwari
R
R
D002244:Carbon / Q000378:metabolism; D006358:Hot Temperature; D007700:Kinetics; D003904:Mitosporic Fungi / Q000201:enzymology* / Q000254:growth & development; D009492:Neurospora crassa / Q000201:enzymology* / Q000254:growth & development; D012995:Solubility; D014198:Trehalase / Q000302:isolation & purification / Q000378:metabolism*
D002244:Carbon; D014198:Trehalase