Which two proteins are referred to as enzymatic carriers?

• A. Ceruloplasmin and Transferrin
• B. Hemopexin and CRP
• C. Albumin and Fibrinogen
• D. C3 and Transferrin

Answer: (A)

The concept here is that some serum proteins not only transport essential metals but also participate in enzymatic reactions related to their metabolism. Ceruloplasmin is a copper-containing enzyme that acts as a ferroxidase, converting Fe2+ (the ferrous form) to Fe3+ so iron can be loaded onto transferrin for transport. Transferrin itself is the primary carrier that ferric iron binds to in the blood and delivers to tissues via transferrin receptors. Together, they form a pair that links enzymatic activity with metal transport, which is why this option is the best fit for “enzymatic carriers.” The other pairs involve proteins that are carriers or immune/clotting components but do not embody this enzymatic–carrier combination.