Figure 2.

Typical steady-state experiments for the determination of λ in WT (A) and Fmr1 null (B) mice illustrating the achievement and maintenance of a constant SA of [³H]leucine (□) over 120 min and the relatively constant arterial plasma leucine concentration (▵) over this interval. The figure also shows the SA of the tRNA-bound leucine (•) in brain at the end of the experiment. In both genotypes, the tRNA-bound leucine SA is considerably below that of the arterial plasma, indicating that there is significant recycling of unlabeled leucine derived from protein breakdown back into the precursor amino acid pool.