Characterization of a bovine synovial fluid lubricating factor. I. Chemical, surface activity and lubricating properties.

A lubricating glycoprotein (PSLF) with an apparent molecular weight of 280 kDa was purified from bovine synovial fluid by anion exchange, molecular sieve chromatography, and density gradient centrifugation. Lubrication was measured under boundary conditions as lowering of the coefficient of friction (mu) between oscillating natural latex and polished glass. Lubricating ability was first observed at a concentration of 200 micrograms/ml and became maximal at 260 micrograms/ml. Hydrophobic interfacial tension measurements indicated that at the former concentration, monolayers of PSLF formed. Sugar digestions showed that lubricating ability depends upon the terminal galactose of the molecule. PSLF is similar if not identical to lubricin. It is proposed that a repulsive hydration force is the molecular mechanism for lubricating activity.