Chemical and Functional Properties of Food Saccharides

© 2004 by CRC Press LLC
FIGURE 16.4 Structure of proteoglycans complex of cartilage. 1, hyaluronic acid; 2, proteoglycan;
3, chondroitin sulfates; 4, protein core; 5, binding protein. (Adapted from Briskey,
E.J. et al., J. Agric. Food Chem., 14, 201, 1966.)
Modifications such as sulfation, epimerization, and deacetylation occur after
polymerization is completed. Apart from differentiation in the number and length
of chains connected to the protein backbone, these modifications contribute to the
structure and type of PG.
Decomposition of GAGs in connective tissue is catalyzed by galactosidases,
glucuronidases, glycosidases, and hyaluronidase. Hyaluronidase decomposes substances
cementing particular fibers and cells. This process facilitates exchange of
matter in the extracellular space. Microorganisms producing hyaluronidase damage
specific immunobarriers responsible for spreading of pathogens such as toxins,
viruses, and bacteria throughout tissues. Primarily, hyaluronidase depolymerizes
large HA molecules into simpler nonreducing polysaccharides. N-Acetylglucosamine
and glucuronic acid are liberated in the subsequent phase.
Hyaluronidase also catalyzes the degradation of other GAGs. Both microbial
hyaluronidase and hyaluronidase from male gonads catalyze hydrolysis of HA. Ch-
4-S and Ch-6-S are decomposed solely by hyaluronidase of male gonads, and none
of these enzymes can decompose DS and KS.
GAGs in animal organisms are distributed in the connective tissue. Together
with other components of the ground substance of the tissue, they fill the space
between collagen, elastin, and reticulin fibers. Sulfated GAGs play a key role in
building structure and mechanical properties of connective tissue. HA which forms
viscous, colloidal aqueous solutions that fill the extracellular space is a lubricant in
joints, filler in eye lens, and shock absorber in disks of vertebral column.
Heparin is a blood anticoagulant, inhibiting formation of thrombin from prothrombin.
Thrombin is responsible for transformation of fibrinogen into fibrin.