Molecular studies of glycogen phosphorylase b from XXXX liver.

@entity1472 @entity535 @entity2707 @entity291 @entity214
Two active isoforms of @entity291 liver phosphorylase with distinct subunit composition have previously been purified (C  mara Artigas, A., Bar  n, C. and Parody-Morreale, A. Prot. Express. Purif. 1994, 5, 157), one showing three @entity214 -PAGE polypeptide bands (molecular mass = 97, 55 and 40 kDa) and the other showing just one (molecular mass = 97 kDa). A molecular mass of 200 kDa has been determined for the native enzymes by gel filtration. @entity535 analyses have been performed in both cases, giving the same results which are similar to those obtained with other phosphorylases. @entity214 -PAGE experiments at different concentrations of the three-band enzyme have suggested a 1:1:1 stoichiometry between the polypeptides. The @entity2707 site is located in the 55 kDa polypeptide and the phosphorylation site in the 40 kDa one. These polypeptides can be generated from the three-band enzyme by tryptic attack in the presence of glycogen without loss of enzyme activity. In the absence of glycogen, 55 kDa and 38 kDa polypeptides are generated, with a significant decrease in activity. We conclude that the three-band enzyme is a dimer composed of an intact monomer and a broken one. The lyotropic salt activation site of the enzyme is near the @entity1472 terminal group.
