Direct Comparisons of Inhibitor Sensitivities of Reverse Transcriptases from Feline and Human Immunodeficiency Viruses

The sensitivities of reverse transcriptases (RTs) from feline immunodeficiency virus (FIV) and human immunodeficiency virus type 1 (HIV) were directly compared. The two enzymes had similar sensitivities to three analogs of dTTP, namely, 3'-azido-3'-deoxythymidine 5'-triphosphate, 2',3'-dideoxythymidine 5'-triphosphate, and 2',3'-dideoxy-2',3'-didehydrothymidine 5'-triphosphate. Each of these analogs demonstrated competitive inhibition of both enzymes. Ki values for inhibition of FIV RT by these three inhibitors were 3.3, 6.7, and 1.8 nM, respectively; Ki values for inhibition of the HIV enzyme were 6.5, 5.9, and 8.3 nM, respectively. Ratios of the Ki for the inhibitor to the Km for the substrate were also determined for each inhibitor, and no differences between the two enzymes greater than threefold were observed. Inhibition constants for 3'-amino-3'-deoxythymidine 5'-triphosphate and 3'-fluoro-3'-deoxythymidine 5'-triphosphate were determined for FIV RT, and these were similar to published values for HIV RT. The activities of three dideoxynucleoside 5'-triphosphates against FIV RT were determined; ddGTP was slightly more potent than ddTTP, whereas both were much more effective than ddCTP. The activity of a noncompetitive inhibitor, phosphonoformate, was also examined with the FIV enzyme; it was much more active with poly(rA)-oligo(dT) as the template-primer than with poly(rC)-oligo(dG) or poly(rI)-oligo(dC).