The British Journal of Rheumatology, Vol 37, 21-26, Copyright © 1998 by British Society for Rheumatology
IM Schwarz and BA Hills
To resolve the apparent conflict between a lubricating glycoprotein,
'lubricin', as the active ingredient in synovial fluid (SF) and surface-
active phospholipid (SAPL) present in SF (and adsorbed to articular
cartilage) as the boundary lubricant reducing friction to such low
physiological levels, lubricin was isolated from bovine SF following the
original procedure of Swann et al. (Arthritis Rheum 1981;24:22-30).
Analysis of the lipid extract by thin-layer chromatography and phosphorus
determination demonstrated a phospholipid component of 11.1 +/- 1.7% (N =
5) which corresponds very closely to the 9.2-13.0% of lubricin which had
hitherto remained unidentified and which has previously been shown to be
transferable to the articular surface to impart lubrication. These results
would appear to resolve any theoretical conflict in that lubricin is,
indeed, an active ingredient within SF. Yet, as a large water-soluble
molecule, it really functions as a carrier for the highly insoluble SAPL
which it deposits on the articular surface as the oligolamellar layer
visualized in previous studies. However, it is this deposited SAPL, rather
than lubricin, which actually lubricates.
ORIGINAL PAPERS
Surface-active phospholipid as the lubricating component of lubricin
Department of Physiology, University of New England, Armidale, NSW, Australia.
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