CHARACTERISTICS OF CELLOBIOSE PHOSPHORYLASE

Abstract

Cellobiose phosphorylase, obtained from cell -free extracts of Clostridium thermocellum, was purified sufficiently to remove known interfering enzymes. The enzyme catalyzes the phos-phorolysis of cellobiose with the formation of equimolar quantities of glucose and glucose 1-phosphate. The reaction is reversible, for equimolar quantities of cellobiose and inorganic phosphate are formed from glucose and glucose 1-phosphate. The equilibrium constant, K= (cellobiose) (phosphate)/(glucose) (glucose 1-phosphate), at pH 7 and 37 C is about 4.3. In addition to catalyzing the synthesis of cellobiose the enzyme apparently is able to catalyze the condensation of glucose 1-phosphate and D-xylose, L-xylose, 2-deoxyglucose, or D-glucosamine. The enzyme is able to catalyze the arsenolysis of cellobiose. Beta-glucose 1-phosphate is unable to replace alpha-glucose 1-phosphate indicating that an inversion occurs in the reaction. On the basis of the inversion and the inability of the enzyme to catalyze the exchange between either cellobiose and D-xylose or glucose 1-phosphate and arsenate, a single displacement mechanism is proposed for the reaction.