Table 5.

Enzyme concentrations

Protein	Concentration (μM) in the stroma	Standard error
AK1+AK2	0.5a	0.2
AK1	0.25
AK2	0.25
AKI–HSDH I+AKII−HSDH II	1.26a	0.6
AKI–HSDH I	0.6
AKII–HSDH II	0.6
ASADH	11.6	3.6
DHDPS1+DHDPS2	3.12a	1.2
DHDPS1	1.5
DHDPS2	1.5
HSK	3.9	1.9
TS1	7.4	1.2
CGS	0.7	0.2
TD	0.36	0.2

Enzyme abundance was measured in the stroma of isolated Arabidopsis chloroplast by ELISA (five independent determinations) using purified recombinant proteins as standards. Crude results, expressed in ng enzyme per mg total stromal proteins, were converted into μM enzyme monomer by assuming a total protein concentration of 400 mg ml⁻¹ in the stroma (Robinson and Walker, 1981).

^aThe two isoforms were equally abundant to within the limits of measurement (see Materials and methods).