Soluble and ribosome-associated protein kinases from wheat embryos

In vitro phosphorylation of serum albumin by two protein kinases: a potential pitfall in protein phosphorylation reactions

Bovine albumin was phosphorylated by both cAMP-dependent protein kinase and casein kinase I to a significant extent. Other albumins were also tested and it was found that the extent of phosphorylation varied with the species of origin of the albumin, but was between 1 and 3 mol phosphate per mole albumin for the cAMP-dependent protein kinase-catalyzed reactions. The phosphorylation occurred at and above pH 7.5 and required the presence of thiol reagents. Phosphoamino acid analyses of bovine albumin showed that it was phosphorylated on at least two serine residues. The phosphorylation could not be demonstrated in vivo.

Purification and characterisation of adenosine-3',5'-phosphate-independent protein kinase from wheat germ

cAMP-independent protein kinase was isolated from the wheat germ and purified to electrophoretic homogeneity. The molecular weight of enzyme was approximately 20,000, Km for ATP was (1 +/- 0.2) x 10(-5) M. V was 215 nmol phosphate mg enzyme-1 min-1, and the isoelectric point was at pH 9.2. The enzyme promotes phosphorylation of casein and crude wheat germ ribosomes.

Resolution and general properties of different types of ribosomal protein kinases in mouse plasmocytoma

Three different types of protein kinases (ATP: protein phosphotransferase, EC 2.7.1.37) were isolated and partially purified from a mouse plasmacytoma microsomal KCl wash fraction, then chromatographed on DEAE cellulose and phosphocellulose. The three protein kinase activities designated by protein kinase I, II and III were characterized with respect to their capacity to utilize [gamma-32P]ATP and [gamma-32P]GTP, to interact with cyclic AMP, stimulation by cyclic AMP, substrate specificity and sedimentation behaviour on glycerol gradient centrifugation. Protein kinase I was found to be cyclic AMP dependent and preferentially phosphorylated histones. Protein kinase II and III were insensitive to cyclic AMP, protein kinase II preferentially phosphorylated histones and the protein(s) of a ribosomal KCl wash fraction eluted from DEAE cellulose between 0.2 and 0.35 M KCl and termed "PPx". Protein kinase III phosphorylated casein and ribosomal proteins to a great extent. Studies with glycerol density gradient centrifugation indicated that protein kinase I sediments as a component of about 4.4 S, protein kinase II of 4.3 S and protein kinase III of 3 S. Chromatography on phosphocellulose of the protein kinases isolated from purified free polysomes showed the same type of protein kinases as those from microsomes. So it appears unlikely that protein kinase I and II were contaminants from the cytosol.

Ribosomal protein as substrate for a GTP-dependent protein kinase from yeast

A protein kinase specific for casein and acidic ribosomal proteins was isolated and partly characterized. It was found that the enzyme utilizes GTP and ATP as phosphoryl donors. Its affinity for ATP was considerably higher than for GTP with the km values of 7.6 X 10(-6)M and 5.5 X 10(-5)M, respectively. Two-dimensional acrylamide gel electrophoresis revealed the phosphorylation of the same ribosomal proteins with either of the [gamma-32P] nucleotides used. It was also shown that one acidic protein (S1 or S2) of 40 S and two acidic proteins (L2 and L3) of 60 S ribosomal subunits were predominantly phosphorylated in vitro. The phosphorylated proteins: L2 and L3 seem to correspond to the proteins of L7 and L12 of E. coli ribosomes. The isolated kinase phosphorylated several basic ribosomal proteins though to a lower extent than the acidic ones.

Phosphorylation of ribosomal proteins from eukaryotes in homologous and heterogous cell-free systems

The phosphorylation of ribosomal proteins from eukaryotes in homologous and heterologous cell-free systems has been studied. The ribosomes and protein kinases from yeast (Saccharomyces cerevisiae, strain Bu), wheat (Triticum vulgare) and rabbit (Orystolagus cuniculus) have been used. It has been found that five ribosomal proteins incorporate gamma-32P from ATP during the incubation of wheat ribosomes with wheat protein kinase. When the phosphorylation of isolated wheat ribosomal proteins was examined more phosphoproteins were detected. These data confirm the suggestion that the ribosomal structure affects the phosphorylation. Probably some ribosomal proteins remain hidden for the action of protein kinase. The results from the crossed experiments show that there is no barrier for phosphorylation of yeast ribosomes with liver protein kinase, of wheat ribosomes with yeast and liver protein kinases and of liver ribosomes with yeast and plant protein kinases. The wheat protein kinase does not phosphorylate the yeast ribosomes under these experimental conditions. Some differences in the set of phosphoproteins obtained with various protein kinases have been detected. These data suggest that the ribosomal protein phosphorylation is not highly species specific although it is not universal.

Protein kinase in pine pollen

Protein kinase (E.C. 2.7.1.37) activity towards both endogenous and exogenous substrates has been detected in pine pollen (Pinus canariensis P. Sm.) and partially purified by DEAE-cellulose chromatography. It seems to be not affected by cyclic AMP.