Human placental sodium-dependent vitamin C transporter (SVCT2): molecular cloning and transport function.
We report here on the cloning and functional characterization of human SVCT2, a sodium-dependent vitamin C (ascorbate) transporter. The hSVCT2 cDNA obtained from a human placental choriocarcinoma cell cDNA library, codes for a protein of 650 amino acids with a predicted molecular mass of 70 kDa. At the level of amino acid sequence, the human SVCT2 exhibits 95% identity to its rat homolog. When functionally expressed in mammalian cells, hSVCT2 induces the transport of ascorbic acid. The transport process induced by hSVCT2 is Na(+)-dependent and is specific for ascorbate. The Michaelis-Menton constant (K(t)) for the transport of ascorbate in cDNA-transfected cells is 69 +/- 5 microM. The relationship between the cDNA-specific uptake rate of ascorbate and Na(+) concentration is sigmoidal with a Na(+):ascorbate stoichiometry of 2:1. Northern blot analysis shows that SVCT2-specific transcripts are present in heart, brain, placenta, and liver and is absent in lung and skeletal muscle. The size of the principal transcript is approximately 7.5 kb.
Rajan
D P
DP
Department of Obstetrics and Gynecology, Medical College of Georgia, Augusta, Georgia, 30912, USA.
Huang
W
W
Dutta
B
B
Devoe
L D
LD
Leibach
F H
FH
Ganapathy
V
V
Prasad
P D
PD
D000595:Amino Acid Sequence; D000818:Animals; D001205:Ascorbic Acid / Q000378:metabolism; D001483:Base Sequence; D001692:Biological Transport; D002460:Cell Line; D002822:Choriocarcinoma; D003001:Cloning, Molecular; D005260:Female; D015723:Gene Library; D006801:Humans; D007700:Kinetics; D008969:Molecular Sequence Data; D029363:Organic Anion Transporters, Sodium-Dependent; D011247:Pregnancy; D011506:Proteins / Q000235:genetics* / Q000378:metabolism*; D051381:Rats; D011994:Recombinant Proteins / Q000378:metabolism; D012964:Sodium / Q000378:metabolism; D060347:Sodium-Coupled Vitamin C Transporters; D013379:Substrate Specificity; D027981:Symporters; D014162:Transfection; D014407:Tumor Cells, Cultured; D014594:Uterine Neoplasms
D029363:Organic Anion Transporters, Sodium-Dependent; D011506:Proteins; D011994:Recombinant Proteins; C555163:SLC23A2 protein, human; C555167:Slc23a2 protein, rat; D060347:Sodium-Coupled Vitamin C Transporters; D027981:Symporters; D012964:Sodium; D001205:Ascorbic Acid