Inhibition and activation of oat leaf calcium-dependent protein kinase by fatty acids

Abstract

Oat leaf Ca 2+-dependent protein kinase (CDPK) was extensively purified from oat leaves by chromatography on DEAE-cellulose, phenyl Sepharose CL-4B, DEAE-Sephacel, Cibacron F3GA-Sepharose CL-6B and Sephacryl S-200. The oat leaf CDPK (mol. wt., 79 000 from gel filtration) is nearly absolutely dependent upon micromolar free Ca 2+ and millimolar Mg 2+ for activity and phosphorylates a variety of substrates including lysine-rich histone, casein, bovine serum albumin, avian myosin light chains and a synthetic peptide corresponding to a phosphorylateable sequence of ribosomal protein S6. The oat leaf CDPK is inhibited by lanthanides, including Gd 3+, Ho 3+, Sm 3+ and La 3+, and is also inhibited by variety of inhibitors of calmodulin and of other plant CDPKs including trifluoperazine, chlorpromzine, and calmidazolium. Behenic acid (IC 50 20 μM) is a potent inhibitor of the enzyme. Other long chain fatty acids inhibit the CDPK and the degree of inhibition decreases with decreasing chain length. Long chain fatty acids (notably the fungal elicitor arachidonic acid) can also activate the oat leaf CDPK in the absence of Ca 2+.