Amino acid incorporation by a cell-free preparation from rat adipose tissue. Effects of fasting

Abstract

Ribosomes were isolated from a postmitochondrial, detergent-treated supernatant fraction prepared either from adipose tissue passed through a tissue press, or from a collection of free fat cells. Optimum conditions for incorporation were established and the kinetics of the system denned with and without artificial messenger RNA. Studies were performed on ribosomes isolated from fed, 24-h fasted, and 48-h fasted animals. There was a progressive reduction in yield and activity (per milligram ribosomal RNA) of ribosomal material recovered from animals fasted up to 48 h. In the presence of poly-U, incorporation by ribosomes from fasted animals returned towards but did not reach the fed level. This return was less complete with ribosomes from 48-h than from 24-h fasted groups although as fasting proceeded, the percentage stimulation produced by poly-U progressively increased. Sucrose density gradient analysis revealed a greater proportion of light ribosome species and a smaller proportion of polysomes in fasted than in fed animals. These results suggest that fasting, in addition to producing a progressive reduction in ribosomal yield, also caused an early loss of messenger RNA or messenger function and later an alteration of ribosome function. The effect of fasting on messenger function could not be explained by alterations in ribonuclease activity.