Comparison of mitochondrial and cytosolic tRNA nucleotidyltransferases from Triticum aestivum

Here we report the partial purification and characterization of wheat mitoc hondrial ATP (CTP):tRNA nucleotidyltransferase (EC 2.7.7.25). Our purificat ion scheme involves ammonium sulfate fractionation and chromatography on an ion-exchange, hydroxyapatite, and affinity columns. Our results indicate th at the enzyme is stable over a broad range of temperatures with highest act ivity at 37 degrees C. High activity is seen at alkaline pH with a maximum at pH 9. The enzyme exhibits maximal activity in the presence of 10 mM MgCl 2 and is inhibited by greater than or equal to 100 mM NaCl. We also show th at a second form of this enzyme exists in the wheat cytosolic fraction. Thi s enzyme shares many features with the mitochondrial enzyme but differs fro m the mitochondrial enzyme in its elution profile from hydroxyapatite and i n its response to manganese.