Figure 7.

The endosome is not the donor compartment. PC12 cells expressing ssHRP^P-selectin were incubated in the presence or absence of a 100-fold excess of HRP antibody for 3 h (preincubatedî). The cells were then stimulated or mock stimulated and chased in the presence of radioiodinated anti-HRP, and postnuclear supernatants were fractionated on glycerol gradients. Levels of ¹²⁵I in individual gradient fractions were then determined using a γ-counter and presented as counts per min normalized by levels of HRP activity in cell homogenates. □, Unstimulated with no preincubation; ▪, stimulated with no preincubation; ○, unstimulated and preincubated; ●, stimulated and preincubated