The fungal teratogen secalonic acid D is an inhibitor of protein kinase C and of cyclic AMP-dependent protein kinase

The teratogenic metabolite secalonic acid D deriving from the ergot-producing, rye-infecting ascomycete fungus Claviceps purpurea and from Penicillium oxalicum is an inhibitor of Ca2+- and phospholipid-dependent protein kinase C (PKC) and of the catalytic subunit of cyclic AMP-dependent protein kinase (cAK) (IC50 values 15 mu M and 12 mu M, respectively). Secalonic acid D also inhibits Ca2+-calmodulin-dependent myosin light chain kinase (MLCK) and plant Ca2+-dependent protein kinase (CDPK). The inhibition of cAK by secalonic acid D is competitive with respect to both peptide substrate and ATP. However, secalonic acid D does not inhibit a high-affinity nucleotide-binding phosphatase from potato. A variety of other naturally-occurring teratogenic agents are not inhibitors of the protein kinases examined.