ISOLATION OF HYALURONATEPROTEIN FROM HUMAN SYNOVIAL FLUID*

Abstract

The high molecular weight components of synovial fluid are hyaluronate and proteins. Hyalu- ronate is synthesized by cells of the synovial membrane, and its concentration in normal human synovial fluid is about 3 mg per g (1). Proteins in synovial fluid appear to be identical with those in serum (2). The protein concentration in normal synovial fluid is about 20 mg per g. A problem of considerable interest is whether hyaluronate in synovial fluid is free or exists as a compound with protein. To answer this question, electrophoresis or ultrafiltration have been used in attempts to separate hyaluronate from the proteins of synovial fluid. Some samples of hyaluronate, isolated from human or bovine synovial fluid by electrodialysis at pH 7.2, and treated with Celite to remove protein impurities, had a molar ratio of nitrogen to hexosamine of 1.00 and so were apparently protein-free (3, 4). Hyaluronate's enormous mo- lecular weight (1 x 106 or more) and even greater molecular volume compared to proteins of synovial fluid account for the retention of hyaluronate on special filters that allow proteins to pass through. In contrast to the products obtained by electrodialysis, hyaluronate isolated from bovine synovial fluid by 19 consecutive ultrafiltrations on sintered glass contained 25 per cent protein (5). It was thought that this protein was firmly bound to hyaluronate, and necessary for the anomalous viscosity of hyaluronate solutions. Later it was shown that over 65 per cent of the protein in this product could be removed by trypsin digestion