A kinetic study of the interaction between glycogen and Neurospora crassa branching enzyme.

The interaction of Neurospora crassa branching enzyme (1,4-alpha-D-glucan:1,4-alpha-D-glucan 6-alpha-(1,4-alpha-glucano)-transferase) [EC 2.4.1.18] with substrate glycogen or amylopectin was studied by affinity electrophoresis. By this method, the dissociation constants (K) of the branching enzyme for oyster glycogen (CL-12.2, OCL-6.3) and for potato amylopectin (CL-20, OCL-12.8) were determined to be 13.3 mM and 0.355 mM, respectively. The affinity of the enzyme to the substrate glycogen increased with the increase of outer chain length (OCL) of the substrate. The thermodynamic parameters of the branching reaction were obtained from the changes of K values of the enzyme-substrate complex at various temperatures. The value of heat change (delta H degree) of the branching reaction for amylopectin was -27.7 kcal/deg.mol. The most suitable length of glucan chain for branching was greater than 12 glucose units.