Objective    To investigate the alterations in uptake function of liver specific transporter OATP-C (organic anion transporting polypeptide C) by mutating positive charge consensus lysine K490T (Lys to Thr) localized on this polypeptide extracellular loop.      Methods    Wild type OATP-C full length cDNA was amplified from human liver mRNA by RT-PCR. Mutation of positive charge to neutral amino acid K490T (Lys to Thr) was made by site-direct mutagenesis technique. The recombinant constructs of wild type and mutated OATP-C cDNA with GFP fusion gene at its C-terminal were generated by subcloning and transfected into HEK293 cells， then cell plasma membrane targeting e

xpression and substrate uptake function were observed.      Results    Both the wild type and mutated OATP-C proteins were highly expressed on HEK293 cell plasma membrane. The uptake of [

3

H

]

estrone sulfat substrates of mutated OATP-C markedly reduced in 5 min by 38.66% as compared with wild type. Analysis of concentration-dependent uptake kinetics demonstrated that the mutants possessed a significantly higher Km value and lower Vmax value than those of wild type.     Conclusion    The conserved positive charge Lys-490 on extracellular loop of OATP-C may be a determinant amino acid in the uptake of organic anion substrates.