Purification and characterization of the major nucleoside triphosphatase from rat liver nuclear envelopes

Nuclear envelopes contain a nucleoside triphosphatase. Hydrolysis of ATP or GTP by this enzyme parallels energy-dependent efflux of poly(A)-containing mRNA from nuclei in vitro. Nucleoside triphosphatase has been purified from highly purified preparations of nuclear envelopes from rat liver by three successive affinity steps. The essentially homogeneous enzyme has an apparent molecular weight of 40,000 as checked by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and displays a rather broad substrate specificity. ATP and GTP are hydrolyzed at nearly equal rates, whereas UTP and CTP are only half as active as substrates. For optimal activity, a one-to-one ratio of a divalent cation (Mg2+, Mn2+, or Ca2+) and the nucleoside triphosphate substrate, an alkaline pH and a temperature of 34 degrees C are required. In contrast to the enzyme associated with nuclear envelopes which is stimulated by synthetic poly(A) and the poly(A) segment of the natural poly(A)-containing mRNA, homogeneous nucleoside triphosphatase is unable to be modulated by this polynucleotide species.