Glycoproteins

complex proteins containing carbohydrates. The molecular weight of glycoproteins ranges from tens of thousands to several million. These materials are present in almost all tissues and fluids of animals, including humans, in plant tissue, and in microorganisms. The glycoproteins include mucins (present in the secretions of all mucous glands, saliva, gastric juice, and cerebrospinal and seminal fluids) and mucoids (present in supportive tissue— bones, cartilage, ligaments—in the vitreous body of the eye, and in egg white). Glycoproteins include many of the blood plasma proteins (ceruloplasmin, orosomucoid, transferrin, and prothrombin), blood group components, immunoglobulins, some enzymes (pancreatic ribonuclease B, taka-amylase), and hormones (thyrotropin and the follicle-stimulating hormone). The hydrocarbon content of glycoproteins ranges from fractions of 1 percent to 80 percent. Their polysaccharide part may contain glucosamine, galac-tosamine, galactose, mannose, and other carbohydrates. According to the amino acid content, the known glycoproteins may be divided into two groups: (1) those containing the usual assortment of amino acids and small amounts of carbohydrates (3 to 40 percent) and (2) those containing a specific assortment of amino acids with predominant amounts of serine and threonine and a high carbohydrate content (60 to 80 percent).