Exogeneous heparin or HS inhibit heparitinase-induced ErbB4 80 kDa fragment formation. A) Small concentrations of heparin slightly enhance the heparitinase-induced ErbB4 80 kDa fragment formation, whereas 1 μg/ml heparin and higher concentrations inhibit ErbB4 80 kDa fragment formation as indicated in lysates of T47D cells. B) Incubation with increasing concentrations of bovine lung heparin only did not have marked effect on cells. N. s., non-specific staining in A and B. C) Both heparin and heparan sulfate inhibited activity of recombinant TACE at high concentrations but displayed some enhancement of enzyme activity at low concentrations D) Heparitinase treatment of living MCF-7 cells enhanced cleavage of fluorescent TACE substrate peptide (p = 6 × 10-11) and the effect of heparitinase could be largely reverted by adding 40 μM TAPI-0 to the incubation medium (p = 10-5). The p-values were calculated with two-tailed pairwise Student's test comparing all time points. The enzyme activity analysis was performed three times with similar results. The data shown represents results from a single assay.