Exergonic reactions produce an energy output. These reactions are exergonic. Similarly, we must add energy to shift from a stable form to an unstable form. We say the protein is phosphorylated. Cells need to dole out energy in tiny subunits.
Enzymes are unchanged by catalyzing a reaction, so they can be re-used.
Product feedback mechanisms. Inhibition via competition, and deconformation. Co-enzymes and Cofactors Smaller organic molecules and metallic ions that assist enzymes and act as transfer agents. Cofactors metallic ions, that serve as binding sites. Iron in cytochrome and hemoglobin.