FIGURE 2.

Metabolism of [3-¹³C]serine by isolated Arabidopsis mitochondria. Shown are ¹³C NMR spectra of WT (A) and serat2;2 (B) mitochondria recorded after a 5-h incubation with [3-¹³]serine. Labeled OAS was detectable only in the WT mitochondrial suspension, and a small proportion of the signal is present as NAS. The peaks at 63.9 and 63.0 ppm are natural abundance signals from mannitol and sucrose, respectively. Shown are averaged time courses for the [3-¹³C]serine signal at 60.9 ppm (n = 3) (C) and the total acetyl[3-¹³C]serine (OAS + NAS) signal (n = 3) (D). Error bars were omitted because the shape of the time courses differed between replicates. ●, WT; ○ serat2;2. The inset in C shows that the WT mitochondria metabolized serine faster than the serat2;2 mitochondria over the first 2.5 h of the time course (expressed as the change in signal intensity relative to the mannitol signal per 15 min/mg if protein). *, p = 0.010. The inset in D shows that the production of total acetyl[3-¹³C]serine (OAS + NAS) over the first 2.5 h of the time course (expressed as signal intensity relative to the mannitol signal per mg of protein) was negligible in the serat2;2 mitochondria compared with the WT mitochondria. *, p = 0.011.