FIGURE 8.

Comparison of the substrate specificity of GMPMT and glycogen phosphorylase. A, 25 μg of GMPMT eluted from DE52 was incubated with [¹⁴C]maltose-1-P for 15 (□) or 30 min (○) in the standard assay mixture described in other figures. Also shown in this figure are results when GMPMT was incubated with [¹⁴C]glucose-1-P (125,000 cpm, 10 nmol) for 15 (■) or 30 min (●) in similar incubation mixtures that also contained buffer, glycogen, and GMPMT. In all cases, glycogen was isolated by methanol precipitation, and its radioactive content was determined. B, a similar set of experiments using [¹⁴C]glucose-1-P for 15 (■) or 30 min (●) and [¹⁴C]maltose-1-P for 15 (□) or 30 min (○) as substrates for glycogen biosynthesis by glycogen phosphorylase. Incubation mixtures in this case were the same as in A and contained 20 μg of protein.