A model for the measurement of whole-body protein turnover incorporating a protein pool with lifetime kinetics.

The hypothesis is proposed that the body contains a pool of protein turning over by lifetime rather than traditional first-order kinetics. The basis of the hypothesis is the observation of a step in the labelling curve or urinary ammonia during constant infusion of 15N]glycine. A four pool model has been constructed with different values for the rate of uptake of tracer into the lifetime pool; the calculated curves of tracer concentration show a step quite similar to that observed experimentally. It is concluded that it is possible, from an experimental curve, to derive an approximate estimate of the relative flux to the lifetime protein pool. Some suggestions are proposed for the physiological nature of this pool.