Effect of nuclear localization signal-receptor interaction on nuclear envelope-associated ATPase activity.

The possibility that interaction of the nuclear localization signal (NLS) with its pore receptor may directly stimulate nuclear envelope-associated ATPase activity and consequently provide energy for protein translocation across the pore has been studied. ATPase activity was assayed after cross-linking of the prototype NLS peptide with its pore receptor, or after preincubation of envelopes with NLS-albumin conjugates. Neither treatment enhanced enzyme activity. A more complex series of events may be required for energy-generation at the nuclear pore.

Differential response of cadmium toxicity towards Mg2(+)-ATPase activity in hepatic and renal nuclear membrane in rats.

Treatment with cadmium chloride (40mg/kg body wt/day) for three days led to a marked inhibition of Mg2(+)-ATPase activity in rat liver nuclear membrane, whereas it stimulated the enzyme in renal nuclear membrane. On 30 days treatment (15 mg/kg body wt/day) the effect was totally different i.e. stimulation of enzyme activity in the liver and inhibition in the kidney tissue. Arrhenius plot analysis of the enzyme activity showed significant increase in phase transition temperature only in liver tissue of rats subjected to acute treatment. Lineweaver Burk plots also showed differential effect of cadmium toxicity on the enzyme activity, i.e. while both Km and Vmax were changed in the liver, there was change only in Km of enzyme from kidney.