Fig. 6. PAK1 and N-WASP are present on enriched melanosome fractions. (a,b) Electron microscopy on human melanosomes (HMS) showed that enriched melanosome factions contained primarily stage III (arrows) and stage IV (arrowhead) melanosomes (a; Magnification, 20,000). Western blotting on HMS for transferrin receptor (b) was performed to assess purity of the preparation. HMS extracts (20 µg) run on a 10% gel for transferrin receptor are negative, suggesting that few contaminating endosomes are present in the melanosome preparation. Positive controls consisted of melanocyte whole cell lysate. (c) Western blots of lysates run on 15% gels (20 µg/lane; PAK1, 70 µg/lane; N-WASP) of human melanosome fraction (HMS) and whole cell lysates of human melanocytes (HMC) for PAK1 and N-WASP are shown. Positive controls consisted of Jurkat cell lysates (PAK1) and rat brain lysates (N-WASP). A strong immunoreactive band for PAK1 and N-WASP at the expected molecular weights are present.