Hyaluronan segment

Fig. 27.—Schematic drawing of a hyaluronan segment. Each disaccharide repeat has the potential to participate in four hydrogen bonds, 1 and 2 across the (1— 4). an< 3 and 4 across the (1— 3)-linkage.

Hyaluronan (HA) is a component of every tissue or tissue fluid in higher animals. The highest concentrations are found in cartilage, vitreous humor, and umbilical cord and even blood contains some HA. At physiologic pH, the molecule has been shown to adopt a helical structure and therefore the molecule can be modeled as a series of helical segments that are connected with flexible segments. However, based on results of solution studies, the molecular structure of HA appears to be more complicated. 

Gong H, Underhill CB, Freddo TF. Hyaluronan in the bovine ocular anterior segment, with emphasis on the outflow pathways. Invest Ophthalmol Vis Sci 1994 35 4328-4332. 

Matsuoka and Cowman [32] proposed the consideration of two simple models to study the hydrodynamic properties of hyaluronan on the basis of inherent viscosity. The first model of the not freely-jointed or non-ideal coil is based on the statistical conformations of polymer chains. Under this model, the intrinsic viscosity [ /] is directly proportional to the volume occupied by mass units of the polymer segments. The volume is filled mainly with solvent and has low density of polymer segments. The second model is the freely-jointed chain model. It is assumed that the chain is more extended and its viscosity corresponds to that of the worm-like chains. The intrinsic viscosity changes as a square of the mean-squared end-to-end distance. Experimental studies of intrinsic viscosity of hyaluronan indicate that short chains act as freely-jointed chains and long chain of hyaluronan behave like the not freely-jointed chains. The molecular weight, at which these two types of behaviour co-exist, is approximately 3.75xl(yDa. The size of the polymer corresponds to a smallest coil of hyaluronan (Figure 4.6). 

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