Myophosphorylase is the muscle isoform of the enzyme glycogen phosphorylase.
This enzyme helps break down glycogen (a form of stored carbohydrate) into glucose-1-phosphate, (not glucose) so that it can be utilized within the muscle cell.
A deficiency is associated with Glycogen storage disease type V, also known as "McArdle's Syndrome".
A case study suggested that a deficiency in myophosphorylase may be linked with cognitive impairment. Besides muscle, this isoform is present in astrocytes, where it plays a key role in neural energy metabolism. A 55-year old woman with McArdle disease has expressed cognitive impairment with bilateral dysfunction of prefrontal and frontal cortex. Further studies are needed to assess the validity of this claim.