Protocatechuic acid

Fluorescence imaging experiments were in 80-500 mM NaCl as noted, 20 mM HEPES (pH 7.4), 0.02% Tween 20, 0.1 mM D-biotin (Invitrogen, Carlsbad, CA, USA), 0.5 mg ml⁻¹ BSA together with 2.2mM protocatechuic acid (Santa Cruz Biotechnology, Santa Cruz, CA, USA) and 37nM protocatechuate-3,4-dioxygenase (Sigma-Aldrich) as oxygen scavengers[58 (link)]. 20 mM Bis-Tris (pH 6.2), 20 mM Tris (pH 8.6) or 20 mM CHES (pH 9.8) was used instead of 20 mM HEPES (pH 7.4) when noted. 20 mM HEPES (pH 7.4), 20 mM Bis-Tris (pH 6.2), 20 mM Tris (pH 8.6) or 20 mM CHES (pH 9.8) contributed 0.008, 0.014, 0.005 or 0.015 M to ionic strength[59 (link)]. For fine-tuning the driving pressure of the flow system in experiments that included measurements below 80 dyn cm⁻², 2.5 × 10–6 w/v 1 μm diameter polystyrene particles (PP-10-10, Spherotech, Lake Forest, IL, USA) were added as flow tracers. Some VWF multimers tethered to the surface appear to become more compact after being stretched repeatedly. The fraction of VWF molecules becoming compact increases at extremely high salt concentrations and extreme pH levels. This compaction is perhaps due to the formation of extra attachments between VWF and the surface near the tether point.