title: Purification and characterization of a heat-stable wheat substrate for wheat embryo calcium-dependent protein kinase.
abstract: A heat-stable wheat protein (WP) that is a good substrate for wheat embryo Ca(2+)-dependent protein kinase (CDPK) was purified from wheat embryo by a procedure involving batchwise anion exchange chromatography on DEAE-cellulose (DE52), passage through Phenyl-Sepharose CL-4B, heat and acid treatment and anion exchange HPLC on a DEAE-5PW column. WP is phosphorylated by CDPK to a stoichiometry of about 0.8 mol phosphoryl per mol WP. The Km for WP is 3.5 microM. WP is phosphorylated by CDPK on Ser residues. [32P]phosphoWP exactly copurifies on SDS-PAGE with WP (59 kDa). Phosphorylation of WP by CDPK is largely Ca(2+)-dependent. The N-terminal amino acid sequence of WP has homology with bacterial azurins. Evidence for two serine phosphorylation sites was obtained from sequencing of phosphopeptides derived from tryptic and chymotryptic digests of phosphoWP. One major site of phosphorylation is inferred to be on a serine within the sequence KKMASMK. WP is one of the best endogenous protein substrates yet found for wheat embryo CDPK. A 59kDa protein is phosphorylated in vivo in sprouting wheat.
authors.affiliation: School of Biochemistry, La Trobe University, Bundoora, Victoria, Australia.
authors.forename: A
authors.initials: A
authors.lastname: Chang
authors.forename: R
authors.initials: R
authors.lastname: Condron
authors.forename: G M
authors.initials: GM
authors.lastname: Neumann
authors.forename: G M
authors.initials: GM
authors.lastname: Polya
mesh_terms: D000595:Amino Acid Sequence; D001400:Azurin / Q000737:chemistry; D001665:Binding Sites; D002118:Calcium / Q000494:pharmacology*; D002918:Chymotrypsin / Q000378:metabolism; D004355:Drug Stability; D006358:Hot Temperature; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000378:metabolism; D010750:Phosphoproteins / Q000737:chemistry / Q000302:isolation & purification* / Q000378:metabolism; D010768:Phosphoserine / Q000378:metabolism; D010940:Plant Proteins / Q000737:chemistry / Q000302:isolation & purification* / Q000378:metabolism; D011494:Protein Kinases / Q000378:metabolism*; D012639:Seeds / Q000201:enzymology*; D017385:Sequence Homology; D013379:Substrate Specificity; D014908:Triticum / Q000737:chemistry* / Q000196:embryology
chemical_list: D010446:Peptide Fragments; D010750:Phosphoproteins; D010940:Plant Proteins; D001400:Azurin; D010768:Phosphoserine; D011494:Protein Kinases; D002918:Chymotrypsin; D002118:Calcium