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A potent inhibitor of protein kinase C (PKC), inhibitor protein-1 (KCIP-1), isolated from sheep brain has been shown to consist of eight isoforms by reverse-phase HPLC. Direct protein sequence analysis has revealed these to be the same as those of 14-3-3 protein, described as an activator of tyrosine and tryptophan hydroxylases involved in neurotransmitter biosynthesis. The N-termini of KCIP-1 isoforms were shown to be acetylated, and secondary structure predictions revealed a high degree of alpha-helix with an amphipathic nature. KCIP-1 showed no inhibitory activity towards protein kinase M (the catalytic fragment of PKC) and had no effect on the activities of three other protein kinases, cAMP-dependent protein kinase, Ca2+/calmodulin-dependent protein kinase II and casein kinase 2. Four forms of KCIP-1 were shown to be substrates for PKC in vitro, but none were phosphorylated by the other protein kinases mentioned above.

Original publication




Journal article


Eur j biochem

Publication Date





453 - 461


14-3-3 Proteins, Amino Acid Sequence, Animals, Brain Chemistry, Calcium-Calmodulin-Dependent Protein Kinases, Chromatography, High Pressure Liquid, Cross-Linking Reagents, Electrophoresis, Polyacrylamide Gel, Molecular Sequence Data, Nerve Tissue Proteins, Phosphorylation, Protein Kinase C, Protein Kinases, Sequence Alignment, Sheep, Spectrometry, Mass, Fast Atom Bombardment, Tyrosine 3-Monooxygenase