Inhibition of Na super(+)K super(+)ATPase activity in membranes of Sindbis virus-infected chick cells

Alterations in intracellular concentrations of Na super(+) and K super(+) in Sindbis virus-infected cells result largely from inhibition of ouabain-sensitive Na super(+)K super(+)ATPase (Na super(+) pump) activity. Here we report that membrane preparations derived from Sindbis virus-infected chick cells exhibit reduced Na super(+)K super(+)ATPase activity, indicating that limitation of cellular factors is not responsible for inhibition of ion transport. In vitro phosphorylation of the Na super(+)K super(+)ATPase by [ super(32)P]orthophosphate or [ gamma - super(32)P]ATP is unaltered in membranes of Sindbis virus-infected cells, indicating that a loss of specific enzymatic functions unrelated to formation of Na super(+) pump phosphoenzyme intermediates occurs during the course of viral infection. However, phosphoenzyme intermediates of the Na super(+)K super(+)ATPase prepared from membranes of Sindbis virus-infected cells are inherently less stable than those prepared with membranes of uninfected cells. The instability of these intermediates in vitro is correlated with an altered capacity of the Na super(+) pump to transport monovalent cations into virus-infected cells. super(22)Na super(+) transport studies reveal enhanced ouabain-sensitive Na super(+) uptake by Sindbis virus-infected cells, suggesting that the Na super(+) pump may catalyze enhanced Na super(+)-Na super(+) exchange in the infected cells. These results indicate that the capacity of the Na super(+)K super(+)ATPase to discriminate between binding of extracellular Na super(+) and K super(+) is specifically altered during the course of infection by Sindbis virus.