So in these reactions, the first substrate binds and changes the enzyme to produce an enzyme substrate intermediate complex. And this can be seen in the following diagram. So let's suppose we have substrate A that binds onto the active side of the enzyme to produce this intermediate. What happens next is some type of group. For example, a phosphoryl group from the molecule A can be transferred onto the active side of that enzyme and that modifies that enzyme. And that's why we have this asterisk the start symbol on top of this intermediate.