摘要：

We have used quantitative fluorescence methods to examine the fate of rhodamine-labeled (R-) after to receptors on and Swiss 3T3 cells. From measurements of fluorescence intensities in cells fixed after incubation with R-, we found that uptake was saturable and that half-maximal uptake occurred at 130 nM R-. Fluorescence measurements on cell extracts of and Swiss 3T3 cells also showed a half-maximal uptake of R-near 130 nM. We estimate that cells can take up 10(6) molecules of R-per hour via . The mobility of on the surface of Swiss 3T3 cells was measured by using fluorescence photobleaching recovery. The two-dimensional effective diffusion coefficient of R-receptors was approximately 8 X 10(-10) cm2 s-1, a value close to that previously obtained for and . Degradation of R-by the cells was followed by using the loss of fluorescence from the 185000-dalton band in --gels. Rhodamine fluorescence was detected in the gels by using a microscope fluorescence spectrophotometer. cells degraded to low molecular weight fragments with a t 1/2 of 15 min. Swiss 3T3 cells degraded about 75% of the with a t 1/2 of 1 h. The remaining 25% remained as the intact 185000-dalton after 24 h. No significant accumulation of large breakdown products was observed in Swiss 3T3 or cells.

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