Glycogen phosphorylase is an enzyme involved in glycogen metabolism that's regulated by phosphorylation. Phosphorylation on serine residues results in more enzyme activity, while the dephosphorylated enzyme has little to no activity. What result would you expect on activity if the serine residues that served as phosphorylation sites on glycogen phosphorylase were mutated to aspartate residues?

• A. No effect on activity, since aspartate residues can be phosphorylated similarly to serine residues.
• B. The enzyme would be completely inactive if it has an Asp residue, since it will no longer recognize its substrate.
• C. The enzyme likely has some activity, since Asp is negatively charged like a phosphoryl group, but activity would not be regulated by phosphorylation.
• D. The enzyme would be mostly inactive, since the enzyme can no longer be phosphorylated.