The synthesis of hyaluronic acid in vitreous: I. Soluble and particulate transferases in hyalocytes

Abstract

The cortical tissue layer of the vitreous, which is contiguous to the retina and ciliary body, contains a uniform population of cells called hyalocytes. Homogenates of hyalocytes isolated from the posterior vitreous were separated into soluble and particulate fractions by ultra-centrifugation, and both fractions were found to contain nucleotide sugar transferase activity. The soluble hyalocyte extract contains endogenous hyaluronic acid, which acts as acceptor of radioactivity from UDP-[ 14 ]C]GlcUA and UDP-[ 14 C]GlcNAc. When endogenous hyaluronic acid is removed and no exogenous acceptor added, the soluble enzyme is able to synthesize oligosaccharide from the added nucleotide sugars, both of which are required for optimal incorporation of radioactivity. The particulate transferase is also able to catalyze the incorporation of radioactivity from UDP-[ 14 C]GlcUA into chromatographically immobile material. Although the soluble transferase showed the same activity whether synthesizing new oligosaccharide or transferring sugar residues to polymeric hyaluronic acid, the particulate transferase evidenced a greater capacity for oligosaccharide synthesis than for catalyzing transfer to polymer.