Involved in the efflux of purine ribonucleosides, such as inosine and guanosine. H(+)(out) + inosine(in) = H(+)(in) + inosine(out) guanosine(in) + H(+)(out) = guanosine(out) + H(+)(in) Belongs to the major facilitator superfamily. DHA1 family. NepI (TC 2.A.1.2.26) subfamily.