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. Author manuscript; available in PMC: 2014 Apr 1.
Published in final edited form as: J Exp Bot. 2012 Jan 25;63(4):1713–1723. doi: 10.1093/jxb/err377

Fig. 4.

Fig. 4

The effect of using ATP versus GTP as co-substrate for phosphorylation assays. Protein kinase assays were performed as described in the Materials and methods using purified protein kinases and their substrates (left panel) or chloroplast extracts (right panel) with ATP or GTP as co-substrate. The calcium-dependent protein kinase CPK4 and histone as substrate served as control for a strictly ATP-dependent kinase, and commercial CK2 and casein as substrate were used as a positive control. The autophosphorylation of CPK4 is indicated by an asterisk and the substrate phosphorylation of histone and casein is indicated by a white triangle. Gel-filtrated stromal extracts (str) incubated with ATP and GTP are shown in lanes 5 and 7, respectively and the phosphorylation of thylakoid membranes (thy) by stromal extracts in the presence of either ATP or GTP is shown in lanes 6 and 8, respectively.