Glycogen phosphorylase catalyzes the first step in glycogen degradation. Glycogen phosphorylase requires:

Pyridoxine (Vitamin B6): The active form of pyridoxine is pyridoxal phosphate. Functions: Transamination reactions Alanine synthetase (heme synthesis) Decarboxylation of histidine to histamine Deamination of serine to pyruvate Glycogen phosphorylase action Conversion of tryptophan to niacin Synthesis of several neurotransmitters One half of the total pyridoxine is bound to muscle glycogen phosphorylase. Ref: Elsevier's Integrated Review Biochemistry By John W. Pelley, 2011, Page 175.