An Altered Version of Glycogen Synthase Is Produced in the Laboratory

Multiple Choice

An altered version of glycogen synthase is produced in the laboratory, with one of its amino acid residues substituted for another. Unlike normal glycogen synthase, the activity of the mutant protein is unaffected by glycogen synthase kinase-3. Which mutation is MOST likely to produce this effect?

A) Cys $\rightarrow$ Ser
B) Ile $\rightarrow$ Thr
C) Ser $\rightarrow$ Ala
D) Cys $\rightarrow$ Met
E) Thr $\rightarrow$ Ser