Abstract
The plasma membrane fraction from leaves of tobacco contains a 54-kDa protein with autophosphorylation activity, and the level of this protein increases after feeding of leaves with sucrose [Ohto and Nakamura (1995) Plant Physiol. 109: 973]. The 54-kDa autophosphorylation protein could not be released from the plasma membrane by treatment with salt or alkali but could be efficiently solubilized by 1% sodium deoxycholate (NaDOC). Ion-exchange chromatography of the NaDOC-solubilized proteins in the presence of octylglucoside separated the 54-kDa autophosphorylation protein into three peaks. The autophosphorylation activity of the 54-kDa protein in peaks I and II increased after feeding of leaves with sucrose. The 54-kDa protein in the peak II fraction was enriched about 125-fold starting from the microsomal membrane fraction. The 54-kDa protein in this fraction phosphorylated histone IIIS in a calcium-dependent manner and cross-reacted with an antibody against a calcium-dependent protein kinase (CDPK) of Arabidopsis thaliana. These results suggest that the 54-kDa protein in the peak II fraction is a novel isoform of CDPK which is associated with the plasma membrane and is inducible by sucrose.
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