15. Which of the following is true of glycogen synthase?
(A) Activation of the enzyme involves a phosphorylation.
(B) It catalyzes addition of glucose residues to the nonreducing end of a glycogen chain by formation of (α1 → 4) bonds.
(C) It uses glucose-6-phosphate as donor of glucose units
(D) The conversion of an active to an inactive form of the enzyme is controlled by the concentration of cAMP.
(E) The enzyme has measurable activity only in liver.