Metalloproteins are proteins that require what for their function?

• A. Proteins with metal ion cofactor
• B. Proteins with lipid molecules
• C. Proteins without any metal
• D. Proteins that are lipoproteins

Answer: (A)

Metalloproteins require a metal ion cofactor to function. The metal sits in the protein’s active site and provides electronic properties that the amino acids alone can’t supply, enabling catalysis or stabilizing substrates. Common metals include iron, zinc, copper, and manganese, each supporting different reactions—iron heme groups for oxygen handling, iron-sulfur clusters for electron transfer, zinc in many hydrolases to polarize water, and so on. Without the metal cofactor, the protein loses its catalytic capability. The other statements describe lipid association or the absence of metal entirely, which don’t define metalloproteins.