Transfer of radioactive materials from radioactively labeled conditioned medium to fixed cells

Transfer of radioactive materials to glutaraldehyde-fixed Ni12Cl cells was observed when fixed cells were incubated in conditioned media of Ni12Cl cells cultured with various radioactive precursors such as glucosamine, fucose or leucine. Radioactivities were not transferred to fixed cells when the conditioned medium was boiled. The transfer decreased drastically by treatments of the medium with trypsin or detergents (dodecylsulfate or deoxycholate). Efficient transfer occurred only at the physiological temperature. No radioactivity was transferred to fixed cells if conditioned media of nonlabeled cells and radioactive precursors including various nucleotide sugars were incubated with fixed cells. The transferring activity in a conditioned medium did not decrease by the dialysis or the centrifugation at 105,000 x g for 2 h, and remained in the supernatant. The activity migrated into the sucrose gradient. Materials transferred to fixed cells were not solubilized by detergents but were released by the treatment with trypsin, indicating transferred materials were covalently associated with fixed cells. Those results suggest that conditioned media thus obtained contain both substrate(s) and enzyme(s) which fixed labels to fixed cells.