title: The turnover of skeletal muscle glycogen phosphorylase studied using the cofactor, pyridoxal phosphate, as a specific label.
abstract: The turnover of glycogen phosphorylase has been measured using the cofactor, pyridoxal phosphate, as a label specific for this enzyme in skeletal muscle. Radiolabelled pyridoxine administered in vivo is incorporated into a protein-bound fraction in skeletal muscle, shown by several criteria to be equivalent to glycogen phosphorylase. This pool of radiolabel disappears slowly with a half-life of 11.9 days, taken to be a good estimate of the intracellular half-life of the enzyme. The use of the cofactor in this fashion minimises overestimation of half-life that results from reincorporation of the label. Further, premature dissociation of the cofactor from native enzyme, which would lead to underestimation of half-life, is unlikely. At the level of sensitivity given by this method there was little evidence for the appearance of pyridoxal phosphate-labelled degradation intermediates of the enzyme.
mesh_terms: D000818:Animals; D007700:Kinetics; D008297:Male; D051379:Mice; D009124:Muscle Proteins / Q000378:metabolism; D009132:Muscles / Q000201:enzymology* / Q000378:metabolism; D006005:Phosphorylases / Q000378:metabolism*; D011732:Pyridoxal Phosphate / Q000378:metabolism*; D014357:Trypsin
chemical_list: D009124:Muscle Proteins; D011732:Pyridoxal Phosphate; D006005:Phosphorylases; D014357:Trypsin