Microsomal membranes isolated from barley roots (Hordeum vulgare L. cv. CM72) contained endogenous protein phosphorylation activities that were greatly enhanced by Mn2+, Mg2+ions also stimulated protein phosphorylation, but to a lesser extent than Mn2+, Ca2+ enhanced Mg2+, but not Mn2+dependent phosphorylation. It is proposed that this strong enhancement by Mn2+ may be due to a greater affinity of Mn2+ than either Ca2+ or Mg2+ for both the Ca2+ and Mg2+ binding sites of certain kinases. Some Mn2+ stimulated kinase activity was eliminated from the membrane by washing with 0.2 mol/L KCl. The KCl extract contained histone and casein kinase activities, and 4 major phospho-proteins that were phosphorylated on serine and threonine residues. Phosphorylation of a 52 kDa polypeptide corresponded with the characteristics of the histone kinase activity and may represent the autophosphorylation of a CDPK-type kinase. Phosphorylation of a 36 kDa polypeptide was Ca2+ stimulated and may represent the autophosphorylation of a different type of unknown kinase. Polypeptides of 18 and 15 kDa had characteristics that suggest they were autophosphorylating subunits of a membrane bound nucleotide di-phosphokinase.
Bibliographical noteFunding Information:
a Funded by USDA competitive grant number 92-37100-7669 to FMD.
- Protein kinase
- Protein phosphorylation
- Root membranes
ASJC Scopus subject areas
- Agronomy and Crop Science
- Plant Science