Table 3.

Effects of Dephosphorylation on SBE Activity in T. aestivum

SBE Activity (μmol min−1mg protein−1)
+ ATP+ APase
Amyloplast stroma213 ± 2054 ± 7
Chloroplast stroma252 ± 1486 ± 6
Amyloplast granule-associated proteins179 ± 19184 ± 21
  • Samples were pretreated with 1 mM ATP or 10 units APase for 20 min at 25°C. Agarose-conjugated APase was removed by centrifugation (plastid stroma), and soluble alkaline phosphatase was removed by anion exchange chromatography (granule-associated extracts). SBE activity was measured using the phosphorylase a stimulation assay. Data shown are the mean ± se of six (plastid stroma) and four (granule-associated proteins) individual preparations, respectively. Control experiments with amyloplast and chloroplast stroma were performed whereby equal volumes of ATP-treated and APase-treated stroma were mixed and incubated for 20 min at 25°C before measurement of SBE activity. Values obtained from the mixing experiments were 138 ± 15 μmol min−1mg protein−1 (amyloplast stroma, n = 3) and 176 ± 21 μmol min−1mg protein−1 (chloroplast stroma, n = 3).