Cholera toxin-peroxidase: changes in surface labeling of glioblastoma cells with increased time in tissue culture.

Cholera toxin coupled to peroxidase yielded a highly specific ultrastructural marker of plasma membrane monosialogangliosides. Studies with cultures of brain and brain tumors suggested that long-term culture of tissue in monolayers results in eventual loss of surface monosialogangliosides.