Glycogen debranching enzyme in bovine brain

Glycogen debranching enzyme was partially purified from bovine brain using a substrate for measuring the amylo-1,6-glucosidase activity Bovine cerebru m was homogenized, followed by cell-fractionation of the resulting homogena te. The enzyme activity was found mainly in the cytosolic fraction. The enz yme was purified 5,000-fold by ammonium sulfate precipitation, anion-exchan ge chromatography, gel-filtration, anion-exchange HPLC, and gel-permeation HPLC. The enzyme preparation had no a-glucosidase or a-amylase activities a nd degraded phosphorylase limit dextrin of glycogen with phosphorylase. The molecular weight of the enzyme was 190,000 and the optimal pH was 6.0. The brain enzyme differed from glycogen debranching enzyme of liver or muscle in its mode of action on dextrins with an alpha -1,6-glucosyl branch, indic ating an amino acid sequence different from those of the latter two enzymes . It is likely that the enzyme is involved in the breakdown of brain glycog en in concert with phosphorylase as in the cases of liver and muscle, but t hat this proceeds in a somewhat different manner. The enzyme activity decre ased in the presence of ATP, suggesting that the degradation of brain glyco gen is controlled by the modification of the debranching enzyme activity as well as the phosphorylase.