Table 2.

Uptake of various markers into sorting endosomes

Marker	Normal	ML-IV
HRP, ng/μg of cell protein	0.70  ±  0.20	0.67  ±  0.10
C5-DMB-LacCer, pmol/μg of DNA	6.10  ±  0.90	6.80  ±  0.20
125I-Tfn,* cpm/μg of protein	0.974  ±  0.083	0.970  ±  0.042

Cells were incubated with the indicated marker for 1 hr at 19°C and washed. For C₅DMB-LacCer and ¹²⁵I-Tfn, cells were then back-exchanged or “acid stripped,” respectively, to remove any marker from the plasma membrane before analysis. 

^*In a typical experiment, each sample contained at least, 1,000–1,500 cpm above background.