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PubMed1977

Purification and properties of a phosphoprotein phosphatase from rat liver.

A phosphoprotein phosphatase (phosphoprotein phosphohydrolase, EC 3.1.3.16) has been partially purified from rat liver homogenates by (NH4)2SO4 and ethanol precipitations followed by DEAE-cellulose and Sepharose 6B chromatography. The phosphoprotein phosphatase is capable of cleaving [32P]phosphate from radiolabelled phosphopyruvate kinase (type L) (EC 2.7.1.40), phosphohistones, and phosphoprotamine. However, it did not detectably dephosphorylate ATP, ADP, DL-phosphorylserine or beta-glycerophosphate. Dephosphorylation of [32P]phosphopyruvate kinase was stimulated by divalent cations and inhibited by ATP, ADP, Fru-1,6-P2, and orthophosphate. Divalene cations could reverse inhibition induced by ADP or ATP. At least one function of the phosphoprotein phosphatase may be to remove phosphate groups from the phosphorylated form of pyruvate kinase in the liver.

Adenosine Triphosphate↗
PubMed2004

In vitro activation of protein kinase C by beta-N-oxalyl-L-alpha,beta-diaminopropionic acid, the Lathyrus sativus neurotoxin.

Beta-N-oxalyl-L-alpha,beta-diaminopropionic acid (L-ODAP) toxicity has been associated with lathyrism; a spastic paraparesis caused by excessive dietary intake of the pulse Lathyrus sativus. We investigated the effect of Lathyrus neurotoxin L-ODAP on protein kinase C (PKC) activity under in vitro conditions. L-ODAP activated phosphorylation activity of purified chick brain PKC. Both lysine-rich (histone III-S) and arginine-rich (protamine sulfate) substrate phosphorylation was enhanced in the presence of L-ODAP. The activation is concentration dependent, and maximal activation is observed at 100 microM concentration. Protamine sulfate phosphorylation was enhanced by 47%, whereas histone III-S phosphorylation was enhanced by 50% over PS/PDBu/Ca2+ dependent activity. The nontoxic D-isomer (D-ODAP) did not affect both histone III-S and protamine sulfate phosphorylation activity. These results indicate that L-ODAP taken up by neuronal cells could also contribute to PKC activation and so be associated with toxicity.

Amino Acids, Diamino↗
PubMed1974

Phosphoprotein phosphatase activity associated with estrogen-induced protein in rat uterus.

Estrogen-induced protein was purified from rat uteri and assayed for several enzymatic activities involved in the metabolism and action of cyclic nucleotides. No adenylate and guanylate cyclase (EC 4.6.1.1 and 4.6.1.2, respectively), protein kinase (EC 2.7.1.33), and cyclic nucleotide binding activities could be demonstrated in three independent preparations of the protein. However, all three preparations exhibited significant phosphoprotein phosphatase activity (EC 3.1.3.16) on phosphorylated protamine and histones F1. This activity is optimal at neutral pH, inhibited by Zn(++), and unaffected by cyclic AMP or cyclic GMP.

Adenylyl Cyclases↗
PubMed1982

Some comparative aspects of regulation of muscle and liver phosphorylase kinase.

The interaction of muscle and liver phosphorylase kinase with some proteins has been studied. It was shown that muscle G-actin has a visible stimulating effect on the dephosphorylated form of muscle phosphorylase kinase. The effect of F-actin on this enzyme is very low. The interaction of phosphorylase kinase with G-actin probably is one of the additional links between glycogenolysis and muscle contraction. To answer the question what subunit(s) of phosphorylase kinase is involved in the interaction with G-actin we studied the influence of actin on the kinase preparations previously activated to a different degree by partial proteolysis with endogenous protease(s) or with trypsin. G-actin has almost no stimulating effect on the preparations of phosphorylase kinase deeply activated by proteolysis (pH 6.8-8.2 activity ratio more than 0.2). The experiments with partial proteolysis allow us to suppose that alpha-subunit is involved in the interaction of phosphorylase kinase with G-actin. Skeletal muscle G-actin activates purified preparations of liver phosphorylase kinase but to a lower degree than muscle enzyme. Brain and liver calmodulin has a low activating effect on liver phosphorylase kinase in the presence of calcium. Calcium-independent action of calmodulin on the preparations of liver phosphorylase kinase is stronger; probably it is connected with a nonspecific effect of this small acidic protein on the liver enzyme. The basic protein protamine has a strong inhibitory effect on liver phosphorylase kinase.

Actins↗
PubMed1975

[Presence of various protein kinases and of partially copurified endogenous substrates in the soluble fraction of an experimental tumor of the rat thyroid gland].

Various fractions containing protein-kinases have been partly purified from supernatant (105 000 g) of an experimental rat's thyroid cancer (1-8 Wollman). These fractions are activated at different levels by cyclic nucleotides and present an unequal affinity for protamine; they phosphorylate an endogenous substrate apparently copurified with the enzyme fractions and adorbed with them on calcium phosphate gel.

Animals↗
PubMed1981

Separation between modulator-dependent protein kinases I and II.

The separation of modulator-dependent protein kinase I from modulator-dependent protein kinase II obtained from the lungs of sexually premature male mice was accomplished by Sephadex G-200 gel filtration. After preincubation of a mouse lung cytosol fraction with arginine-rich histone, theophylline, cyclic GMP and crude protein kinase modulator a cyclic GMP-dependent protein kinase activity peak present in a non-preincubated sample completely disappeared and was replaced by a late-eluted modulator-dependent protein kinase II peak. There was a difference in substrate specificity between modulator-dependent protein kinase I and modulator-dependent protein kinase II despite their similar dependence on crude protein kinase modulator or partially purified stimulatory protein kinase modulator for their maximal activities.

Animals↗
PubMed1990

IL-3-induced activation of protein kinases in the mast cell/megakaryocyte R6-XE.4 line.

A role for second messenger-regulated protein kinases in the early post-IL-3 receptor signal transduction pathway was investigated in the mast cell/megakaryocyte line R6-XE.4. The activity of the calcium- and phospholipid-dependent protein kinase C (PKC) was assessed by the ability of the enzyme to phosphorylate histone H1 in the presence of calcium, diacylglycerol, and phosphatidylserine or after proteolytic activation of PKC with trypsin. In high serum-supplemented cells, but not in cells that were preincubated in serum-deficient media for 6 h, subsequent treatment for 15 min with synthetic IL-3 (10 micrograms/ml) caused up to a sixfold increase in the calcium- and lipid-stimulated histone H1 phosphorylating activity of particulate-associated PKC after fractionation on MonoQ. However, there was no corresponding reduction of cytosolic PKC activity. Therefore, IL-3 appeared to modify the activity of preexisting membrane-associated PKC rather than eliciting its recruitment from the cytoplasm in R6-XE.4 cells. This was in contrast to the situation with FDC-P1 cells, where IL-3 induced PKC translocation. IL-3 also stimulated a cytosolic protein kinase that phosphorylated a synthetic peptide patterned after a phosphorylation site in ribosomal protein S6, but this IL did not alter the activity of cAMP-dependent protein kinase.

Cell Compartmentation↗
PubMed1991

Modulation of cofactor requirement for the activation of protein kinase C by heparin. Possible effect at the regulatory domain.

Heparin was found to stimulate the phosphorylation of histone H1 but not protamine sulfate catalyzed by Ca2+/phospholipid-dependent protein kinase (protein kinase C or PKC). The effect of heparin on histone H1 phosphorylation appeared to be due to an increase in phosphatidylserine affinity for PKC activation in the presence of heparin. This effect of heparin was abolished when trypsinized, cofactor-independent, PKC was employed to phosphorylate histone H1. These studies suggest that heparin acts at the regulatory domain of PKC, and emphasize the importance of the negative charge in influencing the accessibility of the substrate to PKC action.

Animals↗