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THE APPARENT TURNOVER OF MITOCHONDRIA, RIBO‐SOMES AND sRNA OF THE BRAIN IN YOUNG ADULT AND AGED RATS 1
Author(s) -
Menzies R. A.,
Gold P. H.
Publication year - 1972
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1972.tb06212.x
Subject(s) - protein turnover , mitochondrion , biology , rna , protein metabolism , biochemistry , metabolism , protein biosynthesis , medicine , endocrinology , gene
—[ 14 C] orotic acid and [ 3 H] l ‐leucine were injected intraperitoneally into two groups of rats, aged 12 and 24 months, respectively. The apparent turnover of RNA and protein from several subcellular fractions was assessed by following the loss of label from these fractions with time. The curves for apparent turnover of all protein fractions from mitochondria were single exponential curves. Total mitochondrial protein from younger animals had a half‐life of 26.8 days. Two protein subfractions, protein insoluble in cold perchloric acid and chloroform‐methanol (residual protein) and protein soluble in chloroform‐methanol (C–M protein) had similar half‐lives: 26.3 and 26.1 days, respectively. For the older animals the half‐lives were 23.5 days for total protein, 17.4 for residual protein and 30.4 for C–M protein. The difference between the two protein subfractions from mitochondria of the older animals suggests an age‐associated deviation from the synchrony of synthesis and degration of proteins in this organelle. Further deviation from the unit concept of mitochondrial turnover was seen in the apparent turnover of mitochondrial RNA. Mitochondrial RNA had half‐lives of 10.0 and 11.6 days for older and younger animals, respectively, with no significant difference between the groups. No age‐associated difference was observed in the apparent turnover of sRNA. This fraction exhibited a double exponential turnover pattern; the first component in both cases had a half‐life of about 5–8 days and the second component 13–16 days. Ribosomal RNA and protein from both older and younger animals exhibited multiexponential kinetics but both components, RNA and protein, within each age group appeared to turn over synchronously. Average values for apparent turnover of total ribosomes (RNA and protein) were 18.2 days for the older animals and 7.4 days for the younger animals. The age‐associated difference was highly significant P < (0.001).