PH dependence of the kinetic parameters of maltodextrin phosphorylase

Abstract

The pH dependence of the kinetic parameters, Km and Vmax, for maltodextrin phosphorylase have been studied in the pH range 5.6 to 8.5. The data show that ionizable groups in the binary and ternary complexes with average pK values of 6.2 and 7.5 are important for enzyme-substrate binding; the Vmax is affected only by the more acidic group. A conformational transition is suggested to explain the pH dependence of the acidic limb. The involvement of the phosphoryl group of pyridoxal phosphate is discussed.