Identification and biochemical analysis of a homolog of a sulfate transporter from a vanadium-rich ascidian Ascidia sydneiensis samea.
BACKGROUND
Several species of ascidians accumulate extremely high levels of vanadium ions in the vacuoles of their blood cells (vanadocytes). The vacuoles of vanadocytes also contain many protons and sulfate ions. To maintain the concentration of sulfate ions, an active transporter must exist in the blood cells, but no such transporter has been reported in vanadium-accumulating ascidians.


METHODS
We determined the concentration of vanadium and sulfate ions in the blood cells (except for the giant cells) of Ascidia sydneiensis samea. We cloned cDNA for an Slc13-type sulfate transporter, AsSUL1, expressed in the vanadocytes of A. sydneiensis samea. The synthetic mRNA of AsSUL1 was introduced into Xenopus oocytes, and its ability to transport sulfate ions was analyzed.


RESULTS
The concentrations of vanadium and sulfate ions in the blood cells (except for the giant cells) were 38 mM and 86 mM, respectively. The concentration of sulfate ions in the blood plasma was 25 mM. The transport activity of AsSUL1 was dependent on sodium ions, and its maximum velocity and apparent affinity were 2500 pmol/oocyte/h and 1.75 mM, respectively.


CONCLUSIONS
This could account for active uptake of sulfate ions from blood plasma where sulfate concentration is 25 mM, as determined in this study.
Molecular Physiology Laboratory, Department of Biological Science, Graduate School of Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima 739-8526, Japan. ueki@hiroshima-u.ac.jp
Tatsuya
T
Ueki
Nobuaki
N
Furuno
Qiang
Q
Xu
Yuya
Y
Nitta
Kan
K
Kanamori
Hitoshi
H
Michibata
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001692:Biological Transport; D015153:Blotting, Western; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000737:chemistry / Q000235:genetics; D004591:Electrophoresis, Polyacrylamide Gel; D005260:Female; D006801:Humans; D026901:Membrane Transport Proteins / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009865:Oocytes / Q000378:metabolism; D010802:Phylogeny; D017422:Sequence Analysis, DNA; D013431:Sulfates / Q000097:blood / Q000378:metabolism*; D014561:Urochordata / Q000235:genetics / Q000378:metabolism*; D014639:Vanadium / Q000097:blood / Q000378:metabolism*; D014982:Xenopus laevis
D018076:DNA, Complementary; D026901:Membrane Transport Proteins; D013431:Sulfates; D014639:Vanadium