title: The phosphorylation site of Ca(2+)-dependent protein kinase from alfalfa.
abstract: A 50 kDa, calcium-dependent protein kinase (CDPK) was purified about 1000-fold from cultured cells of alfalfa (Medicago varia) on the basis of its histone H1 phosphorylation activity. The major polypeptide from bovine histone H1 phosphorylated by either animal protein kinase C (PK-C) or by the alfalfa CDPK gave an identical phosphopeptide pattern. The phosphoamino acid determination showed phosphorylation of serine residues in histone H1 by the plant enzyme. Histone-related oligopeptides known to be substrates for animal histone kinases also served as substrates for the alfalfa kinase. Both of the studied peptides (GKKRKRSRKA; AAASFKAKK) inhibited phosphorylation of H1 histones by bovine and alfalfa kinases. The results of competition studies with the nonapeptide (AAASFKAKK), which is a PK-C specific substrate, suggest common features in target recognition between the plant Ca(2+)-dependent kinase and animal protein kinase C. We also propose that synthetic peptides like AAASFKAKK can be used as a tool to study substrates of plant kinases in crude cell extracts.
authors.affiliation: Institute of Genetics, Biological Research Center, Hungarian Academy of Sciences, P.O. Box 521, 6701, Szeged, Hungary.
authors.forename: Z
authors.initials: Z
authors.lastname: Olah
authors.forename: L
authors.initials: L
authors.lastname: Bogre
authors.forename: C
authors.initials: C
authors.lastname: Lehel
authors.forename: A
authors.initials: A
authors.lastname: Farago
authors.forename: J
authors.initials: J
authors.lastname: Seprodi
authors.forename: D
authors.initials: D
authors.lastname: Dudits