Effect of sulfation of the tyrosine residues within the GP Ib subunit. The mean velocity (A) and the total number (B) of rolling cells were determined at a wall shear stress of 10 dyn/cm². Sulfation inhibition experiments were completed using LβIXV cells grown in complete or sulfate-depleted media. Values are the mean ± SEM, n = 4. *Differences between means are statistically significant,P < .05.