Interrelation between whole-body turnover rates of RNA and protein.

In our search for new non-invasive methods to determine metabolic and nutritional state, we have identified several specific, modified, urinary one-way catabolites of rRNA, tRNA and mRNA which permit the assessment of the whole-body turnover of these RNA classes. A comparison of the steady-state turnover of RNA and the proteins actin plus myosin (determined using urinary 3-methylhistidine) in preterm infants and adults showed that preterm infants have about 3 times higher average turnover rates per unit body weight than adults of tRNA and rRNA as well as of actin plus myosin, whereas calculated mRNA turnover was 6 times higher in preterm infants than in adults. These as well as our recent observations of RNA turnover in different mammals are compared here with data on whole-body protein turnover and basal metabolic rates (BMR) in different mammalian species including man, for which data are available. The turnover rates of tRNA, rRNA, protein and energy (BMR) can be described by the relation, turnover = const. x body mass (exp.), the extrapolated exponents being 0.69-0.78. This suggests a common underlying principle, possibly energy turnover, as cause for the coordinated whole-body turnover rates of RNA and protein in the steady state.