Figure 3.

Transfected wt-hgB and Δcys-hCgB are sorted to immature secretory granules upon exit from the TGN. PC12 cells transfected with wt-hgB (left) or Δcys-hCgB (right) were pulse labeled with [³⁵S]sulfate for 5 min and chased for 12 min. Postnuclear supernatants were prepared and subjected to sequential velocity and equilibrium sucrose gradient centrifugation. Equal aliquots of equilibrium gradient fractions were analyzed, either after immunoprecipitation (hCgB) or directly (hsPG, rSgII) by SDS-PAGE and phosphoimaging. The graphs show the quantitation of [³⁵S]sulfate-labeled hCgB, hsPG, and rSgII across the equilibrium sucrose gradient (fraction 1, top). The arrows indicate the peak of constitutive secretory vesicles (CV) and immature secretory granules (ISG).