Rice Membranes Contain a Calcium-Dependent Protein Kinase Activity with Biochemical Features of Animal Protein Kinase C

The presence of calcium-dependent protein kinase activities in rice was investigated. Membrane preparations could phosphorylate the MARCKS peptide, a highly specific substrate for animal protein kinase C (PKC). Phosphorylation, strictly dependent on calcium, was specifically antagonized by a peptide whose amino acid sequence corresponds to the inhibitory, pseudosubstrate domain of mammalian PKC. Similar results have been obtained with rice soluble fractions. Addition of inhibitors of mammalian PKC (staurosporine and calphostin C) also inhibited phosphorylation of specific peptide substrates. Western blot analysis with anti-PKC antibodies identified three major bands (90, 87 and 54 kD) in rice membrane-associated proteins.