protein - any of a large group of nitrogenous organic compounds that are essential constituents of living cells; consist of polymers of amino acids; essential in the diet of animals for growth and for repair of tissues; can be obtained from meat and eggs and milk and legumes; "a diet high in protein"

glycoprotein - a conjugated protein having a carbohydrate component

haemoprotein, hemoprotein - a conjugated protein linked to an iron-porphyrin compound

lipoprotein - a conjugated protein having a lipid component; the principal means for transporting lipids in the blood