It can bind calcium ions. So in skeletal muscle tissue, when we contract the calcium ions stored in the sarcoplasm reticulum is basically released into the cytoplasm. And once inside the cytoplasm, the calcium ions can basically bind onto these rep structures and once the calcium ions bind onto the rep structures, that transforms this partially active enzyme into the fully active phosphorlase kinase. And only now can this structure actually carry out this process with full activity. So we see that in order for phosphorylase kinase to actually initiate this process, which in turn initiates glycogen breakdown, this molecule itself must be initiated. And it is initiated by two different processes the phosphorylation of these beta subunits as well as the binding of the calcium ions on these red delta structures.