Purification and some properties of adenosine triphosphate: nicotinamide mononucleotide adenylyltransferace from pig liver

A procedure for the purification of adenosine triphosphate:nicotinamide mononucleotide adenylyltransferase (E.C. 2.7.7.1) from pig liver has been developed. The procedure consists of the isolation of nuclei from a liver homogenate (the enzyme is exclusively localized in the nucleus) and extraction of the enzyme from the nuclei with a NaCI solution . DNA is removed from the NaCI extract with protamine sulfate, and this is followed by heat and ethanol fractionations. The enzyme in the ethanol fraction is further purified by gel filtration on Sephadex G-200, hydroxyapatite column chromatography, and ammonium sulfate fractionation. This purification procedure yields enzyme preparations that can catalyze the synthesis of 3 mu-moles of NAD per min per mg of protein. This represents a 1,000-fold purification over the enzyme activity in nuclei, with a yield of 14%. An enzyme preparation with a specific activity of 1 .69 had at least 6 protein components on polyacrylamide disc gel electrophoresis. The purification procedure was repeatable and has been successfully scaled up to 16 kg of pig liver. From gel filtration studies on Sepharose 6B, it has been determined that the enzyme, as it exists in solutions during the purification procedure, has a Stokes radius of 62.4 A. Other studies have shown that NMN adenylyltransferase can be reversibly inhibited by NaCI in the reaction mixture and that the degree of inhibition is a function of the NaCI concentration . The stability of the enzyme to heat, pH, and ethanol, and the stabilizing effects of dithiothreitol were also investiga