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The retina-specific human ABC transporter (ABCR) functions in the retinal transport system and has been implicated in several inherited visual diseases, including Stargardt disease, fundus flavimaculatus, cone-rod dystrophy, and age-related macular degeneration. We have previously described a general ribonucleotidase activity of the first nucleotide binding domain (NBD1) of human ABCR (Biswas, E. E. (2001)Biochemistry 40, 8181–8187). In this communication, we present a quantitative study analyzing the effects of certain disease-associated mutations, Gly-863 → Ala, Pro-940 → Arg, and Arg-943 → Gln on the nucleotide binding, and general ribonucleotidase activities of this domain. NBD1 proteins, harboring these mutations, were created through in vitrosite-specific mutagenesis and expressed in Escherichia coli. Results of the enzyme-kinetic studies indicated that these mutations altered the ATPase and …