A comparative study in bone and kidney of nucleotide and RNA synthesis

Abstract

1. 1. The synthesis in vivo of precursor AMP and RNA were compared in rat metaphyseal bone and kidney. 2. 2. A simple method is described which permitted the isolation and purification from bone homogenates of native 5′-AMP which would otherwise have been extensively degraded. 3. 3. The kinetics of incorporation of 32P into acid-soluble AMP and into RNA followed a pulse-chase pattern which was qualitatively similar in both organs, and resembled the pattern of RNA labeling in metaphyseal bone in vitro. AMP was labeled to a peak 4 h after injection, while RNA labeling, initially rapid, continued for up to 24 h. 4. 4. Sucrose density gradient centrifugation revealed that rapidly labeled polydisperse RNA, of highest specific activity in the 4–18-S region, approached a maximum by 4 h of labeling; the labeling of 28-S and 18-S RNA, initially of lower specific activity, continued gradually, so that specific activity became relatively uniform by 24 h. 5. 5. Within each organ, [ 32P]RNA nucleotides were of approximately equal specific activity. Also, the distribution of 32P among the mononucleotides was essentially similar in bone and kidney, and did not alter appreciably with time. The radioactive base ratios have therefore been considered a good approximation of the true base ratios. There were consistent quantitative organ differences in the extent of labeling of both AMP and RNA. Renal AMP was uniformly of higher specific activity, especially in the early phase of labeling, than bone AMP. However, despite this precursor relationship, specific activities of bone RNA, component sedimentable species and individual mononucleotides were consistently 2-fold the respective kidney values. These data have been discussed in relation to the relative pool sizes of RNA in bone and kidney.