Photorespiration

The haem group in the enzyme catalase is a non-protein component that is tightly and permanently bound to the protein part of the enzyme. Such non-protein parts that are covalently or firmly attached to the enzyme and essential for its activity are known as prosthetic groups.
- An apoenzyme is the protein part of the enzyme without its non-protein component.
- A coenzyme is a loosely bound organic molecule (often derived from vitamins) that assists enzyme activity.
- A cofactor is a general term that includes both prosthetic groups and coenzymes.
Since the haem group is tightly bound and essential for the functioning of catalase, it is classified as a prosthetic group.