Selective binding of colloidal gold-protein conjugates to secretory granules of granular skin glands and myelin sheaths in the skin of Xenopus laevis.

Colloidal gold-protein conjugates are widely used in immunoelectron microscopical studies as general "second antibody" markers. This report demonstrates that colloidal gold conjugated with goat anti-mouse immunoglobulin G (IgG), protein A, and bovine serum albumin (BSA) binds selectively to secretory granules of granular skin glands and myelin sheaths in the skin of Xenopus laevis. The gold labeling pattern was identical whether goat anti-mouse IgG, protein A, or BSA was used to stabilize the colloidal gold sols. Selective labeling over secretory granules of granular skin glands and myelin sheaths with colloidal gold alone was also observed. Such selective labeling could be prevented by increasing the ionic strength (elevation of NaCl content up to 30%) of the washing buffers and the diluent of the antibody. These results demonstrate that secretory granules of granular skin glands and myelin sheaths in the skin of X. laevis have affinity for colloidal gold-protein conjugates and may bind to the charged gold particles electrostatically.