And this is the process that allows the phosphor fructokinase to actually communicate with the hexokinase and essentially tell it to turn off that first step in glycolysis. And once these two irreversible steps are essentially turned off, that greatly diminishes the rate at which the glycolytic pathway actually takes place. Now, there is one important difference between hexokinases in liver cells and hexokinases in skeletal muscle cells. In liver cells we have this same hexacionase that we also have in muscle cells. But in liver cells we have an important isozyme to this particular hexacinase. Now let's recall what an isozyme is.