Properties of mammalian nuclear-envelope nucleoside triphosphatase

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Abstract
The nucleoside triphosphatase activities of the nuclear envelopes from rat liver, pig liver and SV-40-transformed mouse-embryo [fibroblast] 3T3 cells exhibited similar properties. All 3 preparations hydrolyzed ATP, 2''-dATP, 3''-dATP, GTP, CTP and UTP in the presence of Mg2+, Ca2+, Mn2+ and Co2+ with a pH optimum of 8.0, were sensitive to inhibition by mercurials, arsenicals, quercetin, proflavine and adenosine 5''-[.gamma.-thio]triphosphate and were partially inactivated by exposure to high ionic strength. The kinetic behavior was similar for all substrates irrespective of the source of material. The typical Eadie-Hofstee plot, which was concave upwards at pH 8.0 when the ionic strength is 20 mM, became linear when the pH was increased to 8.5 or the ionic strength to 160 mM. The overall evidence, particularly the labeling of only 1 polypeptide by [.gamma.-32P]ATP, suggests that under the conditions of preparation and assay used only 1 class of nucleoside triphosphatase active sites is detectable in nuclear envelopes. The importance of these results for an understanding of the role of the enzyme in vivo is discussed.