Which conjugated protein type has the highest carbohydrate content?

• A. Glycoproteins
• B. Mucoproteins
• C. Proteoglycans
• D. Lipoproteins

Answer: (C)

Proteoglycans have the highest carbohydrate content because they consist of a relatively small protein core that is heavily decorated with long glycosaminoglycan chains. These glycosaminoglycans (like chondroitin sulfate and heparan sulfate) are large, repeating sugar units that can make up most of the molecule’s mass, giving a very high carbohydrate-to-protein ratio. Glycoproteins do carry carbohydrate, but the amount is typically less than in proteoglycans. Mucoproteins are highly glycosylated glycoproteins as well, yet their carbohydrate portion generally does not reach the vast mass contributed by glycosaminoglycan chains in proteoglycans. Lipoproteins are defined by their lipid component, so they don’t have a high carbohydrate content.