Phosphorylation of the red blood cell membrane during the active transport of C++.

The phosphorylation of red blood cell membrane fragments (RBCMF) during Ca++ transport was investigated. When red cell membrane fragments are incubated with [gamma-32P]ATP under the experimental condition which minimizes the phosphorylation of Na+-K+-ATPase, RBCMF are labeled in the presence of Mg++ without Ca++. When Ca++ is added, the labeling decreases due to dephosphorylation of RBCMF. The initial reaction of phosphorylation is reversed in the presence of excess ADP. The treatment of RBCMF with n-ethylmaleimide (NEM) does not interfere with the initial phosphorylation reaction, but blocks the dephosphorylation in the presence of Ca++. These data suggest that the enzymatic sequence of the Ca++ transport mechanism may be very similar to that of the Na+ transport mechanism.