Age-dependent decrease in the amount of eukaryotic initiation factor 2 in various rat tissues.
Recent studies have suggested that the decline in protein synthesis that occurs in rat liver and brain during development and aging is associated with a decrease in the activity of eukaryotic initiation factor 2 (eIF-2). One way in which eIF-2 activity could be decreased in tissue extracts would be through a decrease in the activity of the GDP exchange factor, eIF-2B. In the present study, the activity of eIF-2B was measured in tissue extracts and was found to be less in older than in younger rats. Thus a decrease in eIF-2B activity could account for part of the decrease in protein synthesis that occurs during aging. Another way in which eIF-2 activity could be decreased would be through a decrease in amount of the protein. Therefore the amount of eIF-2 in various tissues was quantified by protein immunoblot analysis. We found that the amount of eIF-2 relative to total protein tended to fall with increasing age. Furthermore, eIF-2 content was directly proportional to the rate of protein synthesis in the tissues examined. Finally, slot-blot analysis of polyadenylated RNA revealed no significant change in the relative abundance of eIF-2 alpha mRNA with age. The last-mentioned experiments suggest that the synthesis of eIF-2 may be regulated through changes in the deficiency of translation of eIF-2 alpha mRNA rather than through changes in gene transcription.
Kimball
S R
SR
Department of Cellular and Molecular Physiology, College of Medicine, Pennsylvania State University, Hershey 17033.
Vary
T C
TC
Jefferson
L S
LS
D000375:Aging / Q000378:metabolism*; D000818:Animals; D001921:Brain / Q000254:growth & development / Q000378:metabolism; D015852:Eukaryotic Initiation Factor-2 / Q000378:metabolism*; D007668:Kidney / Q000254:growth & development / Q000378:metabolism; D008099:Liver / Q000254:growth & development / Q000378:metabolism; D008168:Lung / Q000254:growth & development / Q000378:metabolism; D008297:Male; D009929:Organ Size; D009928:Organ Specificity; D010649:Phenylalanine / Q000378:metabolism; D014176:Protein Biosynthesis; D012313:RNA / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D011865:Radioisotope Dilution Technique; D051381:Rats; D011919:Rats, Inbred Strains; D013154:Spleen / Q000254:growth & development / Q000378:metabolism; D014316:Tritium
D015852:Eukaryotic Initiation Factor-2; D012333:RNA, Messenger; D014316:Tritium; D010649:Phenylalanine; D012313:RNA