THE PROSTHETIC GROUP OF PHOSPHORYLASE

Publisher Website
Google Scholar
Abstract
Muscle phosphorylase a and phosphorylase b contain stoichiometric amounts of firmly bound pyridoxal-5-phosphate (4 and 2 moles per mole of enzyme, respectively) which can be removed by treatment of the enzyme with acid in the presence of ammonium sulfate, followed by washing of the precipitated protein with alkaline ammonium sulfate solution. The enzyme, after removal of pyridoxal-5-phosphate, is catalytically inactive. Reactivation occurs when the enzyme is incubated for 30 minutes at 30[degree] with amounts of pyridoxal-5-phosphate slightly greater than those removed from the protein. Pyridoxaline-5-phosphate and free pyridoxal cannot replace pyridoxal-5-phosphate. The question of what is the mechanism of action of pyridoxal-5-phosphate in the catalytic process remains to be answered.