Dephosphorylation of Human Erythrocyte Membranes Induced by Sendai Virus

Phosphorylated human erythrocyte membranes were prepared by incubation of either intact cells with ³²P-labeled inorganic phosphate or erythrocyte ghosts with [γ-³²P] ATP. Forty to seventy percent of total ³²P counts found in membrane preparations were bound to membrane proteins. Incubation of phosphorylated erythrocyte ghosts with Sendai virus at 37 °C causes rapid membrane dephosphorylation which releases between 20 and 50% of the bound phosphate from the membranes. Under these conditions, Sendai virus induces leakage of the residual hemoglobin left in the erythrocyte ghosts after the hemolysis process. The initial rates of dephosphorylation obey a first-order kinetics and rate constants of 1 × 10^-7 s^-1/HAU to 2.5 × 10^-7 s^-1/HAU were calculated for the viral process. The membrane's endogenous dephosphorylation rates were found to be about five times slower than virus-induced dephosphorylation. A specific virus-cell interaction is essential for stimulation of membrane dephosphorylation as the virus fails to induce dephosphorylation either of neuraminidase-treated erythrocyte ghosts or in the presence of specific antiviral serum. Mg²⁺ and Ca²⁺ ions are required for induction of membrane dephosphorylation by the virus. In the presence of EDTA both self- and virus-induced dephosphorylation are abolished, while in the presence of EGTA and Mg²⁺ only the virus-induced dephosphorylation is inhibited. It appears that Ca²⁺ affects the maximal rate of dephosphorylation obtained at saturating Mg²⁺ concentration. Ca²⁺ does affect, but to a much lesser extent, the apparent K_m(Mg). The ionophore A-21387 + Ca²⁺, as well as various hemolytic reagents such as prymnesin (5000 hemolytic units) and Triton X-100 (0.5%), fail to mimic the virus-specific membrane dephosphorylation.