And the 14th amino acid position is a serene amino acid. So this one has a serine 14 and this one also has a seren 14. And phosphorase kinase can use two ATP molecules to actually attach the phosphoryl groups on the two seren 14 molecules to basically form phosphorase A. And that's what we mean by an interconvertible form. We can go from phosphorase B to phosphorylase A bidactivity of phosphorase kinase, but this requires ATP molecules. Now let's discuss when phosphorase B predominates and when phosphorase A actually predominates in our body.