Practice question

Endosomal maturation involves Rab conversion progressive luminal acidification orchestrated by vacuolar V-type ATPase multisubunit rotary pump hydrolyzing ATP pumping protons generating pH early endosome 6.0-6.5 late 5.5-6.0 lysosome 4.5-5.0. Gradient critical sorting function beyond hydrolysis activation many ligand-receptor complexes exhibit pH dependent affinity due histidine protonation altering charge complementarity. Examples: LDL separates from LDL receptor pH below 6 releasing particle for lysosomal degradation while receptor recycles via retromer, mannose-6-phosphate receptors release lysosomal enzymes upon protonation binding pocket, transferrin releases Fe3+ upon protonation carbonate while apotransferrin remains bound retained high affinity acidic pH. Dissociation allows physical separation receptors segregate narrow recycling tubules via SNX while liberated ligands continue lysosome catabolism. Without acidification bafilomycin or weak base ammonium chloride pH rise sorting fails LDL remains bound preventing recycling and signaling. Clathrin assembly independent acidity, proteasomal degradation cytosolic, mitochondria fusion unrelated pH-triggered endosomal dissociation ensuring efficient cargo segregation and receptor reuse essential homeostasis.