Characterization of trehalose phosphorylase from Schizophyllum commune.
During growth on d-glucose, the basidiomycete Schizophyllum commune produces an intracellular alpha,alpha-trehalose phosphorylase. Specific phosphorylase activity increases steadily during the exponential growth phase, up to a maximum of approx. 0.08 unit/mg of protein, and decreases after the available d-glucose in the medium has been fully depleted. The variation with time of the concentrations of intracellular alpha,alpha-trehalose and Pi is reciprocal to that of trehalose phosphorylase activity, indicating that the enzyme makes temporary use of the pool of alpha, alpha-trehalose (approx. 0.42 mmol/g dry cell) via phosphorolysis. The enzyme has been purified, 150-fold, to homogeneity in 55% yield and characterized. It is a monomeric 61 kDa protein, which seems to lack regulation at the level of enzyme activity. The enzyme catalyses the reversible phosphorolysis of alpha,alpha-trehalose into alpha-d-glucose 1-phosphate and alpha-d-glucose in the absence of cofactors, with a catalytic-centre activity at 30 degrees C of 14 s(-1). Double-reciprocal analysis of the initial velocities for trehalose phosphorolysis and synthesis yields intersecting patterns, and no exchange reaction occurs between alpha-d-glucose 1-phosphate and the phosphate analogue arsenate. Therefore trehalose phosphorylase operates by a ternary-complex, rather than a Ping-Pong, kinetic mechanism. The specificity constants (kcat/Km) of phosphate (6000 M(-1).s(-1)) and alpha-d-glucose 1-phosphate (3500 M(-1).s(-1)) compared with those of alpha,alpha-trehalose (161 M(-1).s(-1)) and d-glucose (260 M(-1).s(-1)), together with the inhibition by NaCl, which is competitive with respect to phosphate with a Ki of 67 mM, suggest an important role for ionic enzyme-phosphate interactions in the catalytic mechanism of trehalose phosphorylase. The isolated enzyme requires alpha,alpha-trehalose (0.1-0.3 M) for its conformational stability.
Division of Biochemical Engineering, Institute of Food Technology, Universität für Bodenkultur (BOKU), Muthgasse 18, A-1190 Wien, Austria.
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Nidetzky
D004795:Enzyme Stability; D005656:Fungal Proteins / Q000032:analysis* / Q000302:isolation & purification / Q000378:metabolism; D005964:Glucosyltransferases / Q000032:analysis* / Q000302:isolation & purification / Q000378:metabolism; D007700:Kinetics; D012567:Schizophyllum / Q000201:enzymology*; D013379:Substrate Specificity
D005656:Fungal Proteins; D005964:Glucosyltransferases; C023181:alpha,alpha-trehalose phosphorylase