The effect of unilateral nephrectomy on the activity of ribosomes in the remaining kidney.

1. Ribosomes isolated from hypertrophic kidneys were examined at different time intervals after unilateral nephrectomy. The activity of ribosomes measured by [14C] leucine incorporation and synthesis of polyphenylalanine from [14C]Phe-tRNA, was increased after 24 h, whereas changes in the composition of ribosomal protein fractions appeared as early as within 6 hours after the operation. 2. In hypertrophic kidney the content of ribosomes increased but the ratio of free and membrane-bound ribosomes remained practically unaltered. However, the specific activity of free ribosomes was twice as high as that of bound ribosomes. 3. It is concluded that the enhanced activity of free ribosomes is one of the factors responsible for the increased protein synthesis in hypertrophic kidney.