Fig. 2.

Protein kinase activity in chloroplasts: Ca²⁺ dependency and the effect of the protein kinase inhibitor purvalanol B (PurB). (A) Ca²⁺-dependent phosphorylation of RuBisCO-depleted stromal proteins from pea chloroplasts. The extracted proteins were incubated with radioactively labelled ATP in the absence or presence of CaCl₂ and/or EGTA. The insert shows a protein kinase assay in the presence of 5 mM EGTA and 5 mM CaCl₂ or MgCl₂, respectively. (B) Ca²⁺-dependent phosphorylation of stromal proteins from Arabidopsis chloroplasts. (C and D) The effect of the protein kinase inhibitor PurB on pea protein kinases. A RuBisCO-depleted stromal extract and a total leaf extract were incubated with radioactively labelled ATP in the absence or presence of 100 μM PurB. Ø=control reaction without inhibitor.