Activation of the heme-stabilized translational inhibitor of reticulocyte lysates by calcium ions and phospholipid.

AUTOR(ES)

De Haro, C

RESUMO

Hemin-supplemented reticulocyte lysates can be activated for translational inhibition by addition of Ca2+ or phospholipid. The fact that this inhibition is prevented or decreased in both cases either by the Ca2+ chelator EGTA or by polymyxin B, an inhibitor of the recently described Ca2+- and phospholipid-dependent protein kinases, suggests the involvement of both Ca2+ and phospholipid in this activation. The inhibition by Ca2+ or phospholipid is accompanied by phosphorylation of the 38-kilodalton subunit of the eukaryotic initiation factor 2 (eIF-2) and the 90-kilodalton band of the heme-controlled translational inhibitor (HCI) and can be reversed by high concentrations of eIF-2 or GTP. When incubation is conducted at 30 degrees C, the inhibition produced by Ca2+ is not reversed by EGTA after 15 min. However, at 20 degrees C, Ca2+ inhibition can be fully reversed as late as 90 min from the start of incubation and phosphorylation of the eIF-2 alpha-subunit is correspondingly decreased. These results are consistent with the idea that, like heme deprivation, the activation by Ca2+ and phospholipid promotes the first step of the reaction pro-inhibitor in equilibrium reversible inhibitor leads to irreversible inhibitor and suggest that, in the presence of hemin albeit by a different mechanism, this activation affects the same inhibitor that is activated in the absence of heme--namely, HCI. Whether this activation is direct or indirect--e.g., via a separate Ca2+- and phospholipid-dependent protein kinase--remains to be determined.

Documentos Relacionados

• Mechanism of activation of the heme-stabilized translational inhibitor of reticulocyte lysates by calcium ions and phospholipid.
• Regulation of protein synthesis in rabbit reticulocyte lysates: purification and characterization of heme-reversible translational inhibitor.
• Regulation of protein synthesis in rabbit reticulocyte lysates: characteristics of inhibition of protein synthesis by a translational inhibitor from heme-deficient lysates and its relationship to the initiation factor which binds Met-tRNAf.
• Mechanism of translational control by hemin in reticulocyte lysates.
• Regulation of protein synthesis in rabbit reticulocyte lysates: purification and initial characterization of the cyclic 3':5'-AMP independent protein kinase of the heme-regulated translational inhibitor.