Figure 3.

¹³C labelling differences in alanine of large subunits (LSUs) and small subunits (SSUs) of ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco). Alanine enrichment varied between the cytosol and plastid pools as revealed by labelling with [U-¹³C]-glucose (n = 3, SD). Differences are reflected in isotopomers of both (a) three carbon and (b) two carbon gas chromatography-mass spectrometry (GC-MS) fragments. (c) Together these two fragments can be used to calculate the labelling of specific isotopomers that are indicated by (*) and (**). Alanine (LSU) labelled exclusively in the first carbon (*) represents 77 − 74 = 3% of all alanine isotopomers and is one half of the pool of singly labelled isotopomers. Enrichment of doubly labelled molecules in the second and third positions (**) is 19 − 14 = 5% out of a total pool of 6% and is the predominantly abundant isotopomer ([M+2]⁺ enrichment).