**2.8 Boronate affinity chromatography**

Glycoproteins were puried using PBA-bound agarose (Sigma-Aldrich, Munich, Germany). 500 µl of sample previously diluted (1 : 1) with equilibration buffer (50 mM taurine/NaOH, pH 8.7, containing 3–10 mM MgCl 2 ) was incubated with 200 µl of pre-washed immobilized ligand resin for 1 h on ice and with gentle shaking. After transfer of the resin into 1,5 ml eppendhorf tubes, the non-binding fraction was collected by low speed centrifugation (10 s, 500 × g). The resin was then thoroughly rinsed with equilibration buffer (six washes of 150 µl each) and 1 N NaCl (three washes of 150 µl each). For nal elution of the bound fraction, a total of six washes (150 µl each) with taurine buffer containing 50 mM sorbitol were used. Three successive fractions (150 µl each) were pooled before further analysis.
