Two autosomal recessive forms of this<unk>  occur, childhood-onset and adult-onset. The gene for myophosphorylase, PYGM (the muscle-type of the glycogen phosphorylase gene), is located on chromosome 11q13. According to the most recent publications, 95 different mutations have been reported. The forms of the mutations may<unk> ary between ethnic groups. For example, the R50X (Arg50Stop) mutation (previously referred to as R49X) is most common in North America and western Europe, and the Y84X mutation is most common among central Europeans. The exact method of protein disruption has been elucidated in certain mutations. For example, R138W is known to disrupt to pyridoxal phosphate binding site. In 2006, another mutation (c.13_14delCT) was discovered which may contribute to increased symptoms in addition to the common Arg50Stop mutation. Myophosphorylase Structure The myophosphorylase structure consists of 842 amino acids. Its molecular weight of the unprocessed precursor is 97 kDa. The three-dimensional structure has been determined for this protein. The interactions of several amino acids in myophosphorylase's structure are known. Ser-14 is modified by phosphorylase kinase during activation of the enzyme. Lys-680 is involved in binding the pyridoxal phosphate, which is the active form of<unk> itamin B6, a cofactor required by myophosphorylase. By similarity, other sites have been estimated: Tyr-76 binds AMP, Cys-109 and Cys-143 are involved in subunit association, and Tyr-156 may be involved in allosteric control. Function Myophosphorylase is the form of the glycogen phosphorylase found in muscle that catalyses the following reaction: ((1→4)-alpha-D-glucosyl) (n) + phosphate = ((1→4)-alpha-D-glucosyl) (n-1) + alpha-D-glucose 1-phosphate Failure of this enzyme ultimately impairs the operation of ATPases. This is due to the lack of normal pH fall during exercise, which impairs the creatine kinase equilibrium and exaggerates the rise of ADP.
Glycogen storage disease type V
Glycogen storage disease type III
Glycogen storage disease type 0
Glycogen storage disease type I
Glycogen storage disease type IV
Glycogen storage disease type II
Glycogen storage disease type IX
Essential fructosuria