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#acidic pH

3 public questions tagged with this topic.

Membrane Transportation

Which ATP pump is involved in generating acidic pH inside organelles like lysosomes?

Generating acidic interior in endocytic compartments essential for cargo sorting, iron release from transferrin, ligand receptor dissociation, viral entry and lysosomal hydrolysis demands active proton translocation against roughly two pH units. Main machinery responsible is vacuolar proton ATPase V-type, large composite enzyme about 900 kilodaltons composed of peripheral V1 complex A3B3CDE3FG3H where A3B3 hexamer contains catalytic ATP hydrolysis sites at alternating interfaces, and integral membrane Vo complex including a subunit with two half channels, c-ring of nine to ten copies c, c double prime providing proton binding glutamate essential carboxylates, subunits d, e and accessory Ac45. Hydrolysis drives rotation of central rotor DF coupled to c-ring, moving protonated glutamates from cytosolic half channel to luminal half channel releasing protons inside. Mechanism rotary without phosphoenzyme intermediate, inhibited by bafilomycin macrolide binding Vo. ABC transporters export xenobiotics, P-type Na+/K+ ATPase maintains plasma gradients not acidic organelle pH. Thus V-class proton pump, not ABC, creates acidic pH in lysosomes and related compartments supporting degradative pathways.

Ref: Forgac, V-ATPase Review, Acidification of Lysosomes and Endosomes by V-Class Proton Pump.

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Protein Sorting and Trafficking

The acidic pH in the late endosome causes:

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.

Ref: Maxfield & McGraw, Nat Rev Mol Cell Biol: Endosomal acidification dissociates receptor-ligand complexes.

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Titration of Amino Acids

Which of the following amino acids has a buffering effect in both acidic and basic pH ranges?

Histidine correctly describes the effect or change asked about in this question. In Titration of Amino Acids, understanding cause-and-effect relationships is essential for predicting biological outcomes. Histidine occurs because of specific molecular interactions, thermodynamic principles, or regulatory mechanisms that govern this biological process. The other options (Aspartic acid, Lysine, and Arginine) describe either opposite effects, effects that occur under different conditions, or changes associated with unrelated processes.

Ref: Lehninger Principles of Biochemistry, Nelson & Cox, 8th Ed., Ch. 3

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