Now, the question that I'd like to address in this lecture is what exactly activates phosphoralase kinase? What exactly allows this molecule to carry out this process in the first place? So once again, phosphorase kinase is the enzyme that catalyzes the conversion of phosphorase B in the T state into phosphorlase A, which predominates in the R state. But what exactly activates this phosphorlase kinase? Well, before we look at that question, let's actually discuss what the structure of phosphorase kinase actually is. Well, the structure of this kinase actually consists of four different types of subunits, four different types of polypeptide chains.