13.7
ATP 구동 펌프 III: V형 펌프
V형 펌프는 식물의 액포막, 효모, 동물 세포의 엔도솜 및 리소좀 막, 몇몇 특수 진핵 세포의 원형질막, 일부 원핵생물의 액포막에서 발견되는 ATP 구동 펌프입니다. 이는 ATP 가수분해를 결합하여 농도 구배에 대해 양성자를 운반하는 V1Vo-ATPase라고도 알려져…
Vacuolar 또는 V-type 펌프는 주로 식물 액포, 리소좀 및 엔도솜과 같은 진핵 생물 하위 세포 구획의 막에 존재하는 ATP 구동 펌프의 한 유형입니다.
V형 펌프는V1과 V0의 두 영역이 있는 터빈과 같은 구조입니다.
막관통V0 영역은 a-소단위체와 막에 걸쳐 있는 c-소단위체의 고리를 포함하여 여러 소단위로 구성됩니다.
세포질 V1 영역은 또한 A와 B 소단위가 번갈아 나타나는 헥사머, 로터 및 주변 고정자를 포함한 수많은 소단위로 구성됩니다.
진핵 세포의 리소좀 막에 존재하는 V형 펌프를 생각해 보십시오.
ATP 분자가V1 영역의 헥사메릭 소단위체로 들어가면 ADP와 무기 인산염으로 가수분해됩니다.
ATP 가수분해에서 방출된 에너지는V0 영역의 중심 줄기와 c-고리 소단위체를 회전시킵니다.
세포질의 양성자는 a-subunit의 채널을 통해 들어가 c-ring subunit에 결합합니다.
동시에, a-subunit의 내강을 향한 채널은 양성자를 리소솜으로 방출하여 다른 양성자가 세포질에서 c-subunit을 결합할 수 있는 공간을 만듭니다.
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Q1: Where are V-type pumps located in eukaryotic cells?
V-type pumps are ATP-driven pumps found on membranes of eukaryotic subcellular compartments including plant vacuoles, lysosomes, and endosomes. They also occur on plasma membranes of specialized eukaryotic cells and some prokaryotes. These pumps are essential for maintaining proton gradients across these membrane systems.
Q2: What are the two main structural domains of V-type pumps?
V-type pumps consist of two turbine-like domains: the cytosolic V1 domain, which contains eight subunits including a hexamer of alternating A and B subunits and performs ATP hydrolysis, and the transmembrane V0 domain, which contains at least five subunits and transports protons across the membrane.
Q3: How does ATP hydrolysis drive proton transport in V-type pumps?
When ATP enters the hexameric subunit of the V1 domain, it hydrolyzes into ADP and inorganic phosphate. The energy released rotates the central stalk and c-ring subunits of the V0 domain. This rotation allows protons from the cytosol to bind c-ring subunits and be released into the organelle lumen against the concentration gradient.
Q4: What cellular processes depend on V-type pump function?
V-type pump proton translocation activity is vital for pH homeostasis, endocytosis, protein trafficking, urine acidification, and neurotransmitter release. These pumps maintain proton gradients necessary for proper organellar function and cellular signaling. Dysfunction of these pumps can impair multiple critical cellular processes.
Q5: How do cells regulate V-type pump activity?
Cells regulate V-type pumps through reversible dissociation of V0 and V1 domains triggered by nutrients and growth factors. Disulfide bond formation at cysteine residues of the A-subunit can prevent ATP hydrolysis. In epithelial cells, pump density modulation occurs through reversible fusion of vesicles containing high densities of V-type pumps with the apical membrane.
Q6: What diseases are associated with V-type pump mutations?
Mutations in V-type pump subunits are associated with renal tubular acidosis, osteoporosis, and neurodegenerative diseases. Complete loss of pump function can be lethal, making these pumps critical for survival. Understanding V-type pump dysfunction has identified them as potential drug targets for treating these conditions.
Q7: How does the a-subunit facilitate proton movement in V-type pumps?
The a-subunit of the V0 domain contains two channels: one facing the cytosol where protons enter and bind to c-ring subunits, and another facing the organelle lumen where protons are released. As protons are released into the lumen, space becomes available for new protons to bind from the cytosol, creating a continuous pumping cycle.