Answer:
The amino part
Explanation:
In amino acids, the central carbon is attached by an amino group, a hydrogen, a radical group and an acid group.
The amino part normally is used to bond with another acid group of another amino acid. But there is a hydrogen atom that is left, that is "free".
In proteins, when millions of amino acids are aligned in a chain, in some occasions, there is an amino group near the acid group and they tend to form hydrogen bonds among the hydrogen of the amino with the oxygen of the acid group.
In the enzyme, the near hydrogen of amino group can be attracted by the hydroxyl group of the substrate as the amino and acid groups.
