Figure 4: (a) Schematic illustration of human ABCG2 and its nonsynonymous polymorphisms. SNP data on the polymorphisms of ABCG2 were obtained from the NCBI dbSNP database and recent publications. The variants R482G and R482T are acquired mutations. (b) ATP-dependent transport of hematoporphyrin by ABCG2 and its variants. Plasma membrane vesicles expressing ABCG2 variants (50 g of protein) were incubated with 20 M hematoporphyrin in the presence or absence of 1 mM ATP in the standard incubation medium at 3C for 10 minutes. The ATP-dependent transport of hematoporphyrin is normalized for the amount of ABCG2 protein. Data are from .