proton-coupled folate transporter (heme carrier protein 1, PCFT/HCP1, solute carrier family 46 member 1, G21, SLC46A1, HCP1, PCFT)
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Function
- intestinal proton-coupled high-affinity folate transporter
- intestinal heme transporter
- mediates heme uptake from the gut lumen into duodenal epithelial cells
- iron is then released from heme & transported into the bloodstream
- higher affinity for folate than heme
- KM=1.3 uM for folic acid (at pH 5.5);
- KM=1.5 uM for folic acid (at pH 6.0);
- KM=2.7 uM for folic acid (at pH 6.5);
- KM=6.0 uM for folic acid (at pH 7.0);
- KM=56.2 uM for folic acid (at pH 7.5);
- Optimum pH is 4.0-5.5.
Structure
belongs to the major facilitator superfamily
Compartment
- apical cell membrane, cytoplasm
- localizes to the apical membrane of intestinal cells in iron-deficient cells
- resides in the cytoplasm in iron-replete cells
Alternative splicing
named isoforms=2
Expression
- expressed in kidney, liver, placenta, small intestine, spleen, retina & retinal pigment epithelium
- lower levels found in colon & testis
- very low levels in brain, lung, stomach, heart and muscle
- in intestine, expressed in duodenum with lower levels in jejunum, ileum, cecum, rectum & segments of the colon
Pathology
- defects in SLC46A1 are the cause of hereditary folate malabsorption