Complex sentence: Although the catalytic mechanisms used by glycogen synthase are not well known, structural similarities to glycogen phosphorylase at the catalytic and substrate binding site suggest that the mechanism for synthesis is similar in glycogen synthase and glycogen phosphorylase.
Split into simpler sentences: Although the catalytic mechanisms used by glycogen synthase are not well known. Structural similarities to glycogen phosphorylase at the catalytic and substrate binding site suggest that the mechanism for synthesis is similar in glycogen synthase and glycogen phosphorylase.