The band 3 anion exchange protein (AE1, SLC4A1) exchanges chloride (Cl-) for bicarbonate (HCO3-) across the plasma membrane according to the concentration gradients of the anions (Knauf et al. 1996, Dahl et al. 2003). SLC4A1 may be part of a complex ("metabolon") with carbonic anhydrase II (CA2) which would facilitate the transport of HCO3- (Sterling et al. 2001).
The band 3 anion exchange protein (AE1, SLC4A1) exchanges chloride (Cl-) for bicarbonate (HCO3-) across the plasma membrane according to the concentration gradients of the anions (Knauf et al. 1996, Dahl et al. 2003). SLC4A1 may be part of a complex ("metabolon") with carbonic anhydrase II (CA2) which would facilitate the transport of HCO3- (Sterling et al. 2001).
Compartment:
plasma membrane,
cytosol,
extracellular region
The proteins responsible for the exchange of Cl- with HCO3- are members of the SLC4 (1-3) and SLC26 (3, 4, 6, 7 and 9) transporter families. SLC4A1 (Band 3, AE1, anion exchanger 1) was the first bicarbonate transporter gene to be cloned and sequenced. It is ubiquitous throughout vertebrates and in humans, is the major glycoprotein present on erythrocytes and the basolateral surfaces of kidney cells. Variations in erythroid SLC4A1 determine the Diego blood group system. Mutations in the erythrocyte form of SLC4A1 can cause hereditary spherocytosis type 4 (SPH4; MIM:612653), a disorder leading to haemolytic anaemia (HA). Mutations include V488M and E90K (Ribiero et al. 2000, Bracher et al. 2001). Some mutations in SLC4A1 can cause distal (type1) renal tubular acidosis (dRTA; MIM:179800) (an inability to acidify urine) and include R589H, R589C and S613F (Bruce et al. 1997). Mutations causing dRTA-HA (MIM:611590) include G701D and V850del (Bruce et al. 2000).
The proteins responsible for the exchange of Cl- with HCO3- are members of the SLC4 (1-3) and SLC26 (3, 4, 6, 7 and 9) transporter families. The SLC26 members are discussed under the section "Multifunctional anion exchangers".
SLC4A1 (Band 3, AE1, anion exchanger 1) was the first bicarbonate transporter gene to be cloned and sequenced (Lux et al. 1989). It is ubiquitous throughout vertebrates and in humans, is present on erythrocytes and the basolateral surfaces of kidney cells. The erythrocyte and kidney forms are different isoforms of the same protein (Kollert-Jons et al. 1993). Variations in erythroid AE1 determine the Diego blood group system (Bruce et al. 1994). A more serious consequence of mutated erythroid AE1 is Hereditary spherocytosis (a disorder leading to haemolytic anaemia) (Jarolim et al. 1995). Defects in the kidney form of AE1 cause distal (type1) renal tubular acidosis (an inability to acidify urine) (Bruce et al. 1997).
SLC4A2 (Non-erythroid band 3-like protein, AE2, anion exchanger 2) is widely expressed and is considered to be the 'housekeeping' isoform of the bicarbonate transporters (Demuth et al. 1986). SLC4A3 (Cardiac/brain band 3-like protein, AE3) is expressed in heart and brain (Yannoukakos et al. 1994).
The proteins responsible for the exchange of Cl- with HCO3- are members of the SLC4 (1-3) and SLC26 (3, 4, 6, 7 and 9) transporter families. SLC4A1 (Band 3, AE1, anion exchanger 1) was the first bicarbonate transporter gene to be cloned and sequenced. It is ubiquitous throughout vertebrates and in humans, is the major glycoprotein present on erythrocytes and the basolateral surfaces of kidney cells. Variations in erythroid SLC4A1 determine the Diego blood group system. Mutations in the erythrocyte form of SLC4A1 can cause hereditary spherocytosis type 4 (HSP4; MIM:612653), a disorder leading to haemolytic anaemia (HA). Some mutations in SLC4A1 can cause distal (type1) renal tubular acidosis (dRTA; MIM:179800) (an inability to acidify urine) and dRTA-HA (dRTA with hemolytic anemia) (MIM:611590) (Tanner 2002, Romero et al. 2013).
In capillaries of the lungs Erythrocytes take up oxygen and release carbon dioxide. In other tissues of the body the reverse reaction occurs: Erythrocytes take up carbon dioxide and release oxygen (reviewed in Nikinmaa 1997, Jensen 2004). In the lungs, carbon dioxide (CO2) bound as carbamate to the N-terminus of hemoglobin (HbA) and protons bound to histidine residues in HbA are released as HbA binds oxygen (O2). Bicarbonate (HCO3-) present in plasma is taken up by erythrocytes via the band3 anion exchanger (AE1, SLC4A1) and combined with protons by carbonic anhydrases I and II (CA1, CA2) to yield water and CO2 (reviewed by Esbaugh & Tufts 2006, De Rosa et al. 2007). The CO2 is passively transported out of the erythrocyte by AQP1 and RhAG. HCO3- in plasma is also directly dehydrated by extracellular carbonic anhydrase IV (CA4) present on endothelial cells lining the capillaries in the lung. In non-pulmonary tissues CO2 in plasma is hydrated to yield protons and HCO3- by CA4 located on the apical plasma membranes of endothelial cells. Plasma CO2 is also taken up by erythrocytes via AQP1 and RhAG. Within erythrocytes CA1 and, predominantly, CA2 hydrate CO2 to yield HCO3- and protons (reviewed in Geers & Gros 2000, Jensen 2004, Boron 2010). HCO3- is transferred out of the erythrocyte by the band 3 anion exchange protein (AE1, SLC4A1) which cotransports a chloride ion into the erythrocyte. Also within the erythrocyte, CO2 combines with the N-terminal alpha amino groups of HbA to form carbamates while protons bind histidine residues in HbA. The net result is the Bohr effect, a conformational change in HbA that reduces its affinity for O2 and hence assists the delivery of O2 to tissues.
Carbon dioxide (CO2) in plasma is hydrated to yield protons (H+) and bicarbonate (HCO3-) by carbonic anhydrase IV (CA4) located on the apical plasma membranes of endothelial cells. Plasma CO2 is also taken up by erythrocytes via AQP1 and RhAG. Within erythrocytes CA1 and, predominantly, CA2 hydrate CO2 to HCO3- and protons (reviewed in Geers & Gros 2000, Jensen 2004, Boron 2010). The HCO3- is transferred out of the erythrocyte by the band 3 anion exchange protein (AE1, SLC4A1) which cotransports a chloride ion (Cl-) into the erythrocyte. Also within the erythrocyte, CO2 combines with the N-terminal alpha amino groups of HbA to form carbamates while protons bind histidine residues in HbA. The net result is the Bohr effect, a conformational change in HbA that reduces its affinity for O2 and hence assists the delivery of O2 to tissues.
Erythrocytes circulating through the capillaries of the lung must exchange carbon dioxide (CO2) for oxygen (O2) during their short (0.5-1 sec.) transit time in pulmonary tissue (Reviewed in Jensen 2004, Esbaugh and Tufts 2006, Boron 2010). CO2 bound as carbamate to the N-terminus of hemoglobin and protons (H+) bound to histidine residues in hemoglobin are released as hemoglobin (HbA) binds O2. Bicarbonate (HCO3-) present in plasma is taken up by erythrocytes via the band3 anion exchanger (AE1, SLC4A1) and combined with H+ by carbonic anhydrases I and II (CA1/CA2) to yield water and CO2 (Reviewed by Esbaugh and Tufts 2006). CO2 is passively transported out of the erythrocyte by AQP1 and RhAG. HCO3- in plasma is also directly dehydrated by extracellular carbonic anhydrase IV (CA4) present on endothelial cells lining the capillaries in the lung.