Effect of calcium on structure and function of a hyaluronic acid matrix: Carbon-13 nuclear magnetic resonance analysis and the diffusional behavior of small solutes

Natural-abundance (13)C NMR at 25.16 MHz has been used to study a 2.5% matrix of hyaluronic acid at various degrees of polymerization and at various ionic strengths. Peak assignment is facilitated by comparing proton-decoupled and off-resonance-decoupled spectra of a hyaluronidase-depolymerized matrix with spectra from relevant monosaccharides. In contrast to the spectrum following depolymerization, the spectrum for intact matrix has considerable broadening, particularly for peaks assigned to the N-acetylglucosamine moiety. This is most dramatic for the hydroxymethylene carbon. With the addition of Ca(2+) above 5 mM these broadened peaks narrow and approach the sharpness observed for the hyaluronidase digest. There is no shift in resonance peak positions. These changes are quantitatively less impressive if Na(+) is substituted for Ca(2+). The data suggest the existence of a considerable degree of order in regions of the matrix at physiological concentrations of Ca(2+). Within such a matrix the translational movement of lysine and glucose is enhanced relative to that in a matrix of agarose. Further addition of Ca(2+) abrogates not only matrix order, but the enhanced diffusivity as well.