[Non-specific acid nucleoside triphosphatase from cytosol and chromatin of rat liver: partial purification and general properties].

The nucleoside triphosphatase (EC 3.6.1.15) was isolated from rat liver cytosol and purified 600-fold. The enzyme hydrolyzes all NTPs and dNTPs, splits NDPs and dNDPs at a low rate and does not destroy NMPs and dNMPs. The phosphatase consists of a single subunit with molecular weight of 65 000. The chromatin fraction of the enzyme is fully bound to the membrane, whereas the cytosol fraction contains 15-30% of the membrane-bound enzyme. Both free and membrane-bound phosphatases possess identical functional properties. The enzymatic activity has a pH-optimum of 4.0--4.5, is increased in the presence of Me2+ and is unaffected by ouabain, Triton X-100, N-ethylmaleimide, NaF or DNA, but is inhibited by NaCl, Pi and PPi. The value of Km is equal to 20 microM for TTP splitting. Since the NTP pool is essentially changed throughout the cell cycle, it is suggested that the nucleoside triphosphatase can participate in the nucleotide pool regulation.