Which protein acts as a carrier for copper in the blood?

Ceruloplasmin is the primary copper-carrying protein in the blood. It plays a vital role in the metabolism of copper by binding approximately 95% of the copper in the bloodstream. This protein facilitates the transport of copper to various tissues and organs where it is needed for enzyme function, particularly those involved in iron metabolism, energy production, and antioxidant defense. In addition to its role as a copper carrier, ceruloplasmin also exhibits enzymatic properties that help in the oxidation of iron, thus playing a secondary role in iron homeostasis.

Albumin, while a significant plasma protein, primarily transports a variety of substances including fatty acids and some hormones, rather than being specific for copper. Transferrin is specifically responsible for iron transport in the blood. Haptoglobin's primary function is to bind free hemoglobin released from red blood cells, thereby preventing kidney damage and controlling iron availability from hemoglobin breakdown.

Understanding the specific roles of these proteins is essential in recognizing how metal ion transport and homeostasis work in the body, particularly for trace elements like copper.