Figure 13-47. Sorting of membrane proteins in the endocytic pathway.

Figure 13-47Sorting of membrane proteins in the endocytic pathway

Transferrin receptors mediate nutrient uptake and constitutively cycle between endosomes and the plasma membrane. By contrast, opioid receptors are signaling receptors that—after ligand binding—are down-regulated by endocytosis followed by degradation in lysosomes. Endocytosis of both receptors initiates in the same clathrin-coated pits. They are then delivered to the same early endosomes where their journeys part: transferrin receptors are sorted to the recycling endosomes, whereas opioid receptors are sorted to late endosomes. The micrograph shows both receptors—labeled with different fluorescent dyes—30 min after endocytosis (transferrin receptors labeled in red and opioid receptors labeled in green). At this time, some early endosomes still contain both receptors and are seen as yellow structures (yellow resulting from an overlap of red and green light emitted from the fluorescent dyes). By contrast, recycling and late endosomes are selectively enriched in either transferrin or opioid receptors, respectively—thus appearing as distinct red and green structures. (Courtesy of Mark von Zastrow.)

From: Transport into the Cell from the Plasma Membrane: Endocytosis

Cover of Molecular Biology of the Cell
Molecular Biology of the Cell. 4th edition.
Alberts B, Johnson A, Lewis J, et al.
New York: Garland Science; 2002.
Copyright © 2002, Bruce Alberts, Alexander Johnson, Julian Lewis, Martin Raff, Keith Roberts, and Peter Walter; Copyright © 1983, 1989, 1994, Bruce Alberts, Dennis Bray, Julian Lewis, Martin Raff, Keith Roberts, and James D. Watson .

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