Heparanase is an endo-
glucuronidase expressed in a variety of tissues and cells that selectively cleaves extracellular and cell-surface
heparan sulfate. Here we propose that this
enzyme is involved also in the processing of
serglycin heparin proteoglycan in mouse mast cells. In this process, newly synthesized
heparin chains (60-100 kDa) are degraded to fragments (10-20 kDa) similar in size to commercially available
heparin (Jacobsson, K. G., and Lindahl, U. (1987) Biochem. J. 246, 409-415). A fraction of these fragments contains the specific pentasaccharide sequence required for high affinity binding to
antithrombin implicated with
anticoagulant activity. Rat skin
heparin, which escapes processing in vivo, was used as a substrate in reaction with recombinant human
heparanase. An incubation product of commercial
heparin size retained the specific pentasaccharide sequence, although
oligosaccharides (3-4 kDa) containing this sequence could be degraded by the same
enzyme. Commercial
heparin was found to be a powerful inhibitor (I50 approximately 20 nM expressed as
disaccharide unit, approximately 0.7 nM
polysaccharide) of
heparanase action toward
antithrombin-binding
oligosaccharides. Cells derived from a
serglycin-processing mouse
mastocytoma expressed a
protein highly similar to other mammalian heparanases. These findings strongly suggest that the intracellular processing of the
heparin proteoglycan polysaccharide chains is catalyzed by
heparanase, which primarily cleaves target structures distinct from the
antithrombin-binding sequence.