REDUCING AGENTS MITIGATE PROTEIN-SYNTHESIS INHIBITION MEDIATED BY VANADATE AND VANADYL COMPOUNDS IN RETICULOCYTE LYSATES

Recently, we synthesized and characterized vanadyl saccharides to eval uate the effects of various vanadate and vanadyl complexes, which diff er in their oxidation states on various biomacromolecules and cellular activities (1, 2). Here, we report that both vanadate (+V oxidation s tate) and different vanadyl species (+IV oxidation state) such as vana dyl D-glucose, vanadyl diascorbate, and vanadyl sulfate, impair the fo rmation of polysomes and inhibit the initiation of protein synthesis i n hemin-supplemented rabbit reticulocyte lysates. Vanadate inhibits pr otein synthesis more severely than vanadyl species and is consistent w ith the idea that vanadate is reduced to vanadyl state intracellularly . The inhibition of protein synthesis caused by low concentrations (10 -20 mu M) of vanadate and vanadyl species is effectively mitigated by reducing agents such as dithiothreitol, reduced glutathione (GSH), or reduced pyridine dinucleotide, A significant decrease in the protein s ynthesis inhibition in vanadate-treated lysates by GSH suggests that t he mechanism of protein synthesis inhibition by vanadate is different than the action of other oxidants such as heavy metal ions and oxidize d glutathione, This suggestion is also consistent with the findings th at vanadium compounds do not stimulate phosphorylation of the alpha (a lpha) subunit of initiation factor 2 (eIF2) or decrease the guanine nu cleotide exchange activity of eIF2B, which is required to exchange GDP for GTP in eIF2.GDP binary complex. The reduction of vanadate to vana dyl state and the subsequent complex formation of vanadyl species with the endogenous reducing compounds or with the -SH groups of certain p roteins may be the cause for protein synthesis inhibition in lysates. (C) 1998 Academic Press.