Chemical energy
Active transport proteins have one key distinguishing feature, which is that they use chemical energy to move a substance against its concentration gradient.
Chemical energy is the ability of a chemical substance to be subjected to changes through a chemical reaction in order to change other chemical substances.
Active transport proteins are proteins that transport substances such as small molecules, or another protein against its concentration gradient. Active transport proteins require chemical energy and they change their shape when they bind with the cell’s fuel (ATP molecule).