Mechanism of activation of the heme-stabilized translational inhibitor of reticulocyte lysates by calcium ions and phospholipid.
We have reported previously that calcium ions and phospholipid activate the heme-stabilized proinhibitor form (pro-HCI) of the heme-controlled translational inhibitor (HCI) in reticulocyte lysates and promote the first step of the reaction pro-HCI in equilibrium reversible HCI----irreversible HCI. This suggested the possible involvement of a Ca2+/phospholipid-dependent protein kinase (protein kinase C) in the activation. However, further investigation revealed, among other things, that polyunsaturated fatty acids (e.g., arachidonic acid) were as effective as Ca2+/phospholipid in promoting translational inhibition and phosphorylation of the alpha subunit of the chain-initiation factor eIF-2 and, moreover, HCI activation could be prevented or reversed in either case by NADPH-generating systems or by dithiols. Our results suggest that pro-HCI is activated by lipoperoxides produced in reticulocyte lysates from either phospholipid or polyunsaturated fatty acids; the presence of Ca2+ is required in the former but not in the latter case. The reversible activation of HCI by Ca2+ and phospholipid might suggest a possible modulatory role of Ca2+ in translational control.
de Herreros
A G
AG
de Haro
C
C
Ochoa
S
S
D002118:Calcium / Q000502:physiology*; D004229:Dithiothreitol / Q000494:pharmacology; D004533:Egtazic Acid / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D005231:Fatty Acids, Unsaturated / Q000494:pharmacology; D008054:Lipid Peroxides / Q000494:pharmacology; D009249:NADP / Q000494:pharmacology; D010084:Oxidation-Reduction; D010442:Peptide Chain Initiation, Translational; D010448:Peptide Initiation Factors / Q000378:metabolism; D010743:Phospholipids / Q000494:pharmacology*; D011493:Protein Kinase C; D011494:Protein Kinases / Q000378:metabolism*; D012156:Reticulocytes / Q000502:physiology*; D019892:eIF-2 Kinase
D005231:Fatty Acids, Unsaturated; D008054:Lipid Peroxides; D010448:Peptide Initiation Factors; D010743:Phospholipids; D004533:Egtazic Acid; D009249:NADP; D011494:Protein Kinases; D019892:eIF-2 Kinase; D011493:Protein Kinase C; D002118:Calcium; D004229:Dithiothreitol