Abstract
The subunit structure and molecular weight of the a and b forms of human muscle glycogen phosphorylase were investigated.
1
Electrophoresis in the presence of sodium dodecylsulfate gave a molecular weight of 94 500 for the monomer. When studied at 1 mg/ml and 20 °C by high‐speed sedimentation equilibrium, sucrose density gradient ultracentrifugation and specific activity‐concentration dependence, both a and b forms of the human enzyme were found to exist as dimers.
2
A slight association of human phosphorylase a was observed in the high‐speed sedimentation equilibrium values of the z‐average molecular weight (262000 for Mmacr;zvs 188000 daltons for Mmacr;w). Some association of the a enzyme was also detected by schlieren sedimentation velocity when the enzyme was studied at 5 mg/ml.
3
Human phosphorylase b could be fully associated to tetramer at 20 °C when Pi, Mg2+ and AMP were added but not in the presence of NaF and AMP which were found to be effective in tetramerizing rabbit phosphorylase b.
4
Another important difference from rabbit phosphorylase was the significantly lower proline content of the enzyme from human muscle.
