Reverse transcriptase from avian myeloblastosis virus: A zinc metalloenzyme

Previous postulates of a relationship between a zinc enzyme and the leukemic process (1,2) have led to the identification of the RNA dependent DNA polymerase -- reverse transcriptase -- of avian myeloblastosis virus as a zinc metalloenzyme. Microwave induced emission spectrometry provides a microanalytical system capable of measuring precisely 10^-11 to 10^-14 g atoms of metal in microgram amounts of enzyme, orders of magnitude more sensitive than other, conventional methods. The chromatographic fraction with highest enzymatic activity contains 1.5 × 10^-11 g atoms of zinc per 1.4 μg of protein, corresponding to 1.7 to 1.9 g atoms of zinc per mole of enzyme for a molecular weight previously determined either as 1.6 or 1.8 × 10⁵. The Zn/activity ratio is constant in the active fractions. Copper, iron and manganese are absent, i.e., at or below their limits of detection, 10^-13 to 10^-14 g atoms. Agents known to chelate zinc inhibit the enzyme while their nonchelating isomers do not. The data underline the participation of zinc in nucleic acid metabolism and bear importantly upon the lesions which accompany leukemia and zinc deficiency.