Magnesium‐Dependent stimulation of protein synthesis by the insulin mimic, pervanadate

The insulin mimic, peroxide of vanadate (pervanadate), stimulated 35 S‐methionine incorporation into Xenopus oocyte protein in a Mg 2+ ‐dependent manner. Reducing the extracellular Mg 2+ concentration from 1.0 to 0.1 mM decreased the pervanadate‐stimulated component of incorporation by 35%; with 0.01 mM Mg 2+ or lower, the pervanadate‐stimulated component was abolished. In addition, reducing extracellular Mg 2+ to 0.01 mM inhibited about 50% of the insulinstimulated component of methionine incorporation. Mg 2+ depletion had no effects on incorporation in controls or when protein synthesis was stimulated by Zn 2+ or bovine growth hormone. Thus, not all substances that stimulated protein synthesis showed a dependence on extracellular Mg 2+ . Reducing extracellular Ca 2+ had no effects on methionine incorporation in control cells or in cells stimulated by pervanadate or insulin. When oocytes maintained in a paraffin oil medium were brought into contact with a 0.5 m̈I droplet of buffer containing the Mg 2+ indicator dye, mag‐fura‐2, and pervanadate, apparent droplet Mg 2+ decreased rapidly, indicating net uptake by the cells. Insulin also caused a net uptake of Mg 2+ . In contrast, apparent extracellular Mg 2+ was constant when cells were in contact with droplets containing no effectors. Together, these data indicate that extracellular Mg 2+ , but not Ca 2+ , is involved in the stimulation of protein synthesis by pervanadate, and to a lesser extent by insulin. Pervanadate appears to induce a net uptake of Mg 2+ , and this change in membrane transport may be an early event in signalling the increase in translation. © 1995 Wiley‐Liss, Inc.