During the phosphorolysis of glycogen and starch, glucose-1-phosphate (G1P) is generated. This kit provides a simple, sensitive, and rapid assay method: Glucose-1-phosphate (G1P) is converted under the sequential action of phosphoglucomutase and glucose-6-phosphate dehydrogenase, reducing NADP⁺ to NADPH. By measuring the increase in NADPH at 340 nm, the glucose-1-phosphate (G1P) content in the sample can be calculated.