Purification of a hepatic S6 kinase from cycloheximide-treated Rats

Cycloheximide injection of rats results in the activation of a protein kinase that phosphorylates 40 S ribosomal protein S6. This Ca2+/cyclic nucleotide-independent kinase exhibits chromatographic properties that are indistinguishable from the S6 kinase in H4 hepatoma cells whose activity is stimulated by insulin and growth factors and the S6 kinase that is activated during liver regeneration. The enzyme has been purified 50,000-fold to near homogeneity: a critical step in purification employs a peptide affinity column using a synthetic peptide corresponding to the carboxyl-terminal 32-amino acid residues of mouse liver S6, which encompasses all S6 phosphorylation sites. The purified enzyme is a 70,000-dalton polypeptide that is reactive with azido-ATP. In addition to 40 S ribosomal S6 and the synthetic peptide, the S6 kinase catalyzes rapid phosphorylation of a number of other protein substrates including histone H2b, glycogen synthase, and ATP citrate lyase; this last protein is phosphorylated by S6 kinase in vitro on the same serine residue that is phosphorylated in response to insulin and epidermal growth factor in intact hepatocytes. Moreover, the S6 kinase catalyzes the phosphorylation of a number of hepatic nonhistone nuclear proteins. This S6 kinase probably underlies the increased hepatic S6 phosphorylation observed after cycloheximide treatment, which in turn corresponds to the mitogen-activated S6 kinase.     

Identification and characterization of a phosphorylation-activated, cyclic AMP and Ca2+-independent protein kinase in the brain

A cyclic AMP and calcium-independent protein kinase has been identified and purified from pig brain to near homogeneity. This independent protein kinase was isolated in an inactive form, and activation required ATP and Mg2+. On sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the purified enzyme contains 1 subunit with a molecular mass of about 36 kDa. Although there was no significant phosphorylation of phosphorylase, phosphorylase b kinase, casein, phosvitin, and protamine, this kinase was found to be very active toward myelin basic protein and histones H1, 2A, and 2B. Trypsinolysis completely destroyed the kinase activity, indicating that this is not a protease-activated protein kinase. More interesting, this cAMP and calcium-independent protein kinase can be regulated by its state of phosphorylation. In its non-phosphorylated state, the kinase was essentially inactive but could be fully activated when the enzyme was phosphorylated up to a 1:1 molar ratio. Conversely, partial dephosphorylation of the phosphorylated enzyme was associated with a time-dependent decrease in the kinase activity and a loss of 32P. All the results taken together point out that this kinase is distinguished from all the reported protein kinases and may represent a previously undiscovered protein kinase. The results also provide initial evidence that a cascade activation mechanism may possibly be involved in the regulation of a protein kinase activity which is independent of cAMP and calcium.     

Effect of Mg2+ concentration on the cAMP-dependent protein kinase-catalyzed activation of rabbit skeletal muscle phosphorylase kinase.

Phosphorylase kinase was found to be activated and phosphorylated at 10mM Mg2+ by the cAMP-dependent protein kinase-catalyzed reaction ot much higher levels than observed previously when reactions were carried out in 1 to 2 mM Mg2+ (Cohen, P. (1973) Eur. J. Biochem. 34, 1; Hayakawa, T., Perkin, J.P., and Krebs, E.G. (1973) Biochemistry 12, 574). That the reaction at 10 mM Mg2+ is protein kinase-catalyzed is supported by several observations: (a) the reaction is facilitated by the addition of protein kinase; (b) the reaction depends on cAMP when protein kinase holoenzyme is uded; (c) the reaction is not inhibited by 1 mM ethylene glycol bis(beta-aminoethyl ether) N,N'-tetraacetate which is known to inhibit autoactivation and autophosphorylation of phosphorylase kinase; and (d) the protein inhibitor of protein kinase inhibits this reaction. The phosphorylation and activation of phosphorylase kinase seem to occur in two phases. At low Mg2+ only the first phase is manifested and involves the incorporation of 2 mol of phosphate, 1 mol into each of Subunits A and B. At high Mg2+ additional sites are phosphorylated almost exclusively on Subunit A, with phosphate incorporation approaching the final level of 7 to 9 mol. Enzyme activity at high Mg2+ is 2 to 3 times higher than that observed when activation is studied at low Mg2+. The observation that both casein and type II histone are phosphorylated to the same extent at 1 mM and 10 mM Mg2+ suggested that high Mg2+ may be altering the conformation of phosphorylase kinase thus rendering more phosphorylation sites accessible to protein kinase. Since the phosphorylation of phosphorylase kinase by either the protein kinase-catalyzed or autocatalytic reaction can result in the incorporation of 7 to 9 mol of phosphate, the finding that only about seven sites become phosphorylated by both mechanisms acting together suggest that activation by these two mechanisms may involve common phosphorylation sites.     

Identification of pseudo ‘phosphothreonyl-specific’ protein phosphatase T with a fraction of polycation-stimulated protein phosphatase 2A

Protein phosphatase T from rat liver, so termed due to its activity toward [³²P-Thr]casein and its marked preference for the phosphopeptide Arg-Arg-Ala-Thr(P)-Val-Ala over its phosphoseryl derivative (Donella Deana, A., Marchiori, F., Meggio, F. and Pinna, L.A. (1982) J. Biol. Chem. 257, 8565–8568), is shown here to belong to the family of type 2A protein phosphatase according to Cohen's nomenclature (Ingebritsen, T.S. and Cohen, P. (1983) Eur. J. Biochem. 132, 255–261). In particular, protein phosphatase T is endowed with phosphorylase phosphatase activity that is stimulated by protamine, histone H1 and heparin, it is inhibited by spermine, it does not bind to heparin-Sepharose and it readily dephosphorylates the phosphopeptide Arg-Arg-Leu-Ser(P)-Ile-Ser-Thr-Glu-Ser reproducing the phosphorylation site of the α-subunit of phosphorylase kinase. The M_r of protein phosphatase T determined by gel filtration under non-denaturating conditions is about 150 kDa and its activity ratio toward histone H1 phosphorylated by protein kinase C versus histone H1 phosphorylated by cAMP-dependent protein kinase is unusually high. Some properties of protein phosphatase T, such as its weak binding to DEAE-cellulose and its high stimulation by protamine as compared to a relatively poor stimulation by histone H1, suggest that it may be similar to subtype 2A_o of protein phosphatase 2A.     

Phosphorylation site specificities of glycogen synthase kinases: determination by peptide mapping using high-performance liquid chromatography

A method is described which separates the various phosphorylation sites in glycogen synthase based on reverse phase high-performance liquid chromatography (HPLC) of tryptic 32P-peptides. Using this method we studied the phosphorylation site specificities of the kinases which act on glycogen synthase. The cAMP-dependent protein kinase phosphorylated sites 1a, 1b, and 2, whereas casein kinase II phosphorylated only site 5. Two calcium, calmodulin-dependent kinases, phosphorylase kinase and liver calmodulin-dependent synthase kinase, both phosphorylated site 2, and the latter enzyme also phosphorylated site 1b. A cAMP-independent kinase (kinase 4) purified from liver also specifically phosphorylated site 2. Synthase kinase 3 catalyzed the phosphorylation of only site 3. This HPLC method was also used to establish that all of these sites were subject to phosphorylation in vivo.     

Identification of pseudo 'phosphothreonyl-specific' protein phosphatase T with a fraction of polycation-stimulated protein phosphatase 2A

Protein phosphatase T from rat liver, so termed due to its activity toward [32P-Thr]casein and its marked preference for the phosphopeptide Arg-Arg-Ala-Thr(P)-Val-Ala over its phosphoseryl derivative (Donella Deana, A., Marchiori, F., Meggio, F. and Pinna, L.A. (1982) J. Biol. Chem. 257, 8565-8568), is shown here to belong to the family of type 2A protein phosphatase according to Cohen's nomenclature (Ingebritsen, T.S. and Cohen, P. (1983) Eur. J. Biochem. 132, 255-261). In particular, protein phosphatase T is endowed with phosphorylase phosphatase activity that is stimulated by protamine, histone H1 and heparin, it is inhibited by spermine, it does not bind to heparin-Sepharose and it readily dephosphorylates the phosphopeptide Arg-Arg-Leu-Ser(P)-Ile-Ser-Thr-Glu-Ser reproducing the phosphorylation site of the alpha-subunit of phosphorylase kinase. The Mr of protein phosphatase T determined by gel filtration under non-denaturating conditions is about 150 kDa and its activity ratio toward histone H1 phosphorylated by protein kinase C versus histone H1 phosphorylated by cAMP-dependent protein kinase is unusually high. Some properties of protein phosphatase T, such as its weak binding to DEAE-cellulose and its high stimulation by protamine as compared to a relatively poor stimulation by histone H1, suggest that it may be similar to subtype 2Ao of protein phosphatase 2A.     

In vitro phosphorylation of the tumor suppressor gene RB protein by mitosis-specific histone H1 kinase

The major components of the mitosis-specific histone H1 kinase are CDC2 kinase and cyclin and the consensus amino acid sequence for phosphorylation by this enzyme has been proposed. We have noted the presence of such sequences in six sites of the tumor suppressor gene RB protein and determined whether or not RB protein is in fact phosphorylated by this kinase. Highly purified enzyme was used for this purpose. HeLa cell extracts immunoprecipitated with anti-RB antiserum as well as RB proteins expressed in E. coli cells were shown to be phosphorylated by this kinase in vitro. Synthetic peptides for the six expected sites were also phosphorylated. These results suggest the possibility that the function of RB protein is regulated by CDC2 kinase.     

Purification of a protein histidine kinase from the yeast Saccharomyces cerevisiae. The first member of this class of protein kinases

An enzyme of molecular weight 32,000 comprising a single subunit has been isolated from whole cell extracts of the yeast Saccharomyces cerevisiae. In vitro, the enzyme transfers the gamma phosphate of ATP to a protein substrate, histone H4, to produce an alkali-stable phosphorylation. Modification of the substrate histidine with diethylpyrocarbonate prevented phosphorylation. Phosphoamino acid analysis of the phosphorylated substrate showed the presence of 1-phosphohistidine. Hence, the isolated enzyme is a protein histidine kinase. A novel assay for acid-labile alkali-stable protein phosphorylation was used in the purification of the kinase activity to a final specific activity of 2,700 nmol/15 min/mg. The purified enzyme phosphorylates specifically histidine 75 in histone H4 and does not phosphorylate histidine 18 nor histidine residues in any other core histone. Steady state kinetic data are consistent with an ordered sequential reaction with Km values for Mg-ATP and histone H4 of 60 and 17 microM, respectively. The protein histidine kinase requires a divalent cation such as Mg2+, Co2+, or Mn2+ but will not use Ca2+, Zn2+, Cu2+, Fe2+, spermine, or spermidine. This is the first purification of an enzyme that catalyzes N-linked phosphorylation in proteins.     

Site-specific phosphorylation of tyrosine hydroxylase after KCl depolarization and nerve growth factor treatment of PC12 cells

The phosphorylation and activation of tyrosine hydroxylase was examined in PC12 cells following depolarization with KCl or treatment with nerve growth factor. Both treatments activate tyrosine hydroxylase (TH) and increase enzyme phosphorylation. Site-specific analysis of the tryptic phosphopeptides of TH isolated from [32P]phosphate-labeled PC12 cells demonstrated that the major phosphorylated peptide (termed "H25") did not contain any of the previously reported phosphorylation sites. Phosphoamino acid analysis of this peptide demonstrated that the phosphorylated residue was a serine. Synthetic tryptic peptides containing putative phosphorylation sites were prepared, and subjected to high performance liquid chromatography analysis and isoelectric focusing. The tryptic phosphopeptide containing serine 31 comigrated with the H25 peptide during both of these analytical techniques. The tryptic phosphopeptide produced by the phosphorylation of tyrosine hydroxylase by the recently discovered proline-directed protein kinase and the phosphorylated synthetic phosphopeptide TH2-12 are clearly separated from H25 by this analysis. We conclude that serine 31 is phosphorylated during KCl depolarization and nerve growth factor treatment of PC12 cells and that this phosphorylation is responsible for the activation of tyrosine hydroxylase. Since this site is not located in a sequence selective for any of the "classical" protein kinases, we suggest that a novel protein kinase may be responsible for the phosphorylation of this site. Since serine 31 has a proline residue on the carboxyl-terminal side, the possibility that this kinase may be related to the recently reported proline-directed protein kinase is discussed. Other sites that are also phosphorylated on TH during KCl depolarization include serine 19, which is known to be phosphorylated by calmodulin-dependent protein kinase II. A schematic model for the regulation of tyrosine hydroxylase activity by phosphorylation of the NH2-terminal regulatory domain is presented.     

Mammalian growth-associated H1 histone kinase: a homolog of cdc2+/CDC28 protein kinases controlling mitotic entry in yeast and frog cells.

Mammalian growth-associated H1 histone kinase, an enzyme whose activity is sharply elevated at mitosis, is similar to cdc2+ protein kinase from Schizosaccharomyces pombe and CDC28 protein kinase from Saccharomyces cerevisiae with respect to immunoreactivity, molecular size, and specificity for phosphorylation sites in H1 histone. Phosphorylation of specific growth-associated sites in H1 histone is catalyzed by yeast cdc2+/CDC28 kinase, as shown by the in vitro thermal lability of this activity in extracts prepared from temperature-sensitive mutants. In addition, highly purified Xenopus maturation-promoting factor catalyzes phosphorylation of the same sites in H1 as do the mammalian and yeast kinases. The data indicate that growth-associated H1 kinase is encoded by a mammalian homolog of cdc2+/CDC28 protein kinase, which controls entry into mitosis in yeast and frog cells. Since H1 histone is known to be an in vivo substrate of the mammalian kinase, this suggests that phosphorylation of H1 histone or an H1 histone counterpart is an important component of the mechanism for entry of cells into mitosis.     

Autophosphorylation of the alpha subunit of phosphorylase kinase from rabbit skeletal muscle

The autophosphorylation of the alpha subunit of phosphorylase kinase occurs simultaneously at multiple sites during incorporation of the first mol of phosphate. The predominant and initial autophosphorylation site on this subunit is different than the major site phosphorylated by cAMP-dependent protein kinase, which also phosphorylates multiple sites, as evidenced by two-dimensional phosphopeptide maps. All of the sites on the alpha subunit phosphorylated by cAMP-dependent protein kinase comigrate on peptide maps with autophosphorylation phosphopeptides; however, several phosphopeptides observed after autophosphorylation are not evident following phosphorylation by cAMP-dependent protein kinase. The phosphopeptide maps of the alpha subunit are the same whether autophosphorylation is carried out at pH 6.8 or 8.2 or whether MnATP is used instead of MgATP; there is only a slight difference in the maps brought about by EGTA-insensitive autophosphorylation. The autophosphorylation is shown to be an intrinsic activity of the phosphorylase kinase molecule; this conclusion is based on the observed copurification of the autophosphorylation activity with activities toward phosphorylase b and kappa-casein and the unaltered influence of various effectors on these activities throughout different sequential adsorption chromatography purification steps. Additional support to that already in the literature that the initial autophosphorylation events are predominantly intramolecular is gained by showing that previously autophosphorylated enzyme has little ability to catalyze the phosphorylation of nonphosphorylated enzyme.     

The substrate specificity of adenosine 3'':5''-cyclic monophosphate-dependent protein kinase of rabbit skeletal muscle.

The known amino acid sequences at the two sites on phosphorylase kinase that are phosphorylated by cyclic AMP-dependent protein kinase were extended. The sequences of 42 amino acids around the phosphorylation site on the alpha-subunit and of 14 amino acids around the phosphorylation site on the beta-subunit were shown to be: alpha-subunit Phe-Arg-Arg-Leu-Ser(P)-Ile-Ser-Thr-Glu-Ser-Glx-Pro-Asx-Gly-Gly-His-Ser-Leu-Gly-Ala-Asp-Leu-Met-Ser-Pro-Ser-Phe-Leu-Ser-Pro-Gly-Thr-Ser-Val-Phe(Ser,Pro,Gly)His-Thr-Ser-Lys; beta-subunit, Ala-Arg-Thr-Lys-Arg-Ser-Gly-Ser(P)-VALIle-Tyr-Glu-Pro-Leu-Lys. The sites on histone H2B which are phosphorylated by cyclic AMP-dependent protein kinase in vitro were identified as serine-36 and serine-32. The amino acid sequence in this region is: Lys-Lys-Arg-Lys-Arg-Ser32(P)-Arg-Lys-Glu-Ser36(P)-Tyr-Ser-Val-Tyr-Val- [Iwai, K., Ishikawa, K. & Hayashi, H. (1970) Nature (London) 226, 1056-1058]. Serine-36 was phosphorylated at 50% of the rate at which the beta-subunit of phosphorylase kinase was phosphorylated, and it was phosphorylated 6-7-fold more rapidly than was serine-32. The amino acid sequences when compared with those at the phosphorylation sites of other physiological substrates suggest that the presence of two adjacent basic amino acids on the N-terminal side of the susceptible serine residue may be critical for specific substrate recognition in vivo.     

Multisite phosphorylation of a synthetic peptide derived from the carboxyl terminus of the ribosomal protein S6

The synthetic peptide AKRRRLSSLRASTSKSESSQK (S6-21) which corresponds to the carboxyl-terminal 21 amino acids of human ribosomal protein S6 was synthesized and tested as a substrate for S6/H4 kinase purified from human placenta. The specific activity of the enzyme with the synthetic peptide and 40 S ribosomes was 45 and 23 nmol/min/mg, respectively. The S6/H4 kinase activity with S6-21 was greater than the enzyme activity with any other substrate tested, including histones, protamine, and casein and several other synthetic peptides. The phosphorylation of the peptide was not inhibited by inhibitors of several other proteins kinases. S6/H4 kinase catalyzed the phosphorylation of three major sites in the synthetic peptide and the 40 S ribosomes. A fourth site in S6-21 was phosphorylated more slowly. The principal phosphorylation sites were serines in the acidic carboxyl-terminal domain of the peptide. A serine (Ser-7 or -8) in the amino-terminal domain was phosphorylated at approximately 25% the rate of the carboxyl-terminal domain serines. The data suggest that multiple S6 kinases may be required to phosphorylate S6 at all five sites which are modified in vivo.     

Phospholipase C activity in plasma membranes isolated from lapine synovial cells in monolayer culture

Two phosphorylase kinase activities were resolved by DEAE-cellulose chromatography. The main activity peak was enriched 2800-fold, the minor appeared to be an aggregate of the enzyme. Phosphorylase kinase also phosphorylated histone and casein with no changes in phosphorylation ratios throughout the preparation steps but was most active on yeast phosphorylase. The molecular weight was 29000 +/- 2000. ATP, UTP, GTP served as substrates while CTP was inactive. Mg-ions activated the kinase without inhibition at high concentrations (30 mM). In addition to this cAMP-independent kinase, cAMP-dependent protein kinase also phosphorylated phosphorylase. The catalytic subunit and phosphorylase kinase were not identical since the latter was not inhibited by yeast cAMP binding protein.     

Specific substrate for histone kinase II: a synthetic nonapeptide

Based on the previously determined intrinsic substrate specificity of histone kinase II, a nonapeptide was synthesized which was a specific substrate for this enzyme. The Vmax value of phosphorylation of the peptide (Ala-Ala-Ala-Ser-Phe-Lys-Ala-Lys-Lys-amide) was about the same as that for H1 histone and the apparent Km for the phosphorylation of the peptide was 0.2 mM, an order of magnitude higher than that for H1 histone. H1 histone inhibited the phosphorylation of the peptide, while the peptide did not inhibit the phosphorylation of H1 histone. In the crude extracts of calf thymus, spleen and liver, histone kinase II was the only enzyme which phosphorylated the synthetic peptide. The rate of phosphorylation of this peptide was used to determine the activity of histone kinase II in the crude extracts of several tissues obtained from different species.     

The phosphorylation site of Ca2+-dependent protein kinase from alfalfa

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 Ca²⁺-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.     

Control of phosphorylase kinase in the isolated glycogen particle by Ca2+-Mg2+ synergistic activation and cAMP-dependent phosphorylation

The isolated glycogen particle provides a means to examine the regulation of glycogen metabolism with the components organized in a functional cellular complex. With this system, we have studied the control of phosphorylase kinase activation by Ca2+ and cAMP. Contrary to a previous report (Heilmeyer, L. M. G., Jr., Meyer, F., Haschke, R. H., and Fisher, E. H. (1980) J. Biol. Chem. 245, 6649-6656), phosphorylase kinase became activated during incubation of the glycogen particle with MgATP2- and Ca2+. Part of this activation could be attributed to the action of the cAMP-dependent protein kinase; however, it was not possible to quantitatively correlate activation with phosphorylation in the presence of Ca2+ and Mg2+ due to a large, but uncertain, contribution of synergistic activation caused by these ions. This latter activation had properties similar to those described by King and Carlson (King, M. M., and Carlson, G. M. (1980) Arch. Biochem. Biophys. 209, 517-523) with the purified enzyme, and its occurrence also explains why phosphorylase kinase activation in the glycogen particle was not observed previously. The cAMP-dependent activation of phosphorylase kinase in the glycogen particle has been characterized. It occurred in a similar manner when either the cAMP-dependent protein kinase or cAMP was added, thus indicating that the phosphorylation sites of phosphorylase kinase complexed in the glycogen particle were accessible to endogenous or exogenous enzyme. In the glycogen particle, both the alpha and beta subunits were phosphorylated by the cAMP-dependent protein kinase, but the alpha subunit dephosphorylation appeared to be preferentially regulated by Ca2+. The activity of phosphorylase kinase in the glycogen particle is regulated by the phosphorylation of both the alpha and beta subunits.     

The regulatory and basal phosphorylation sites of hormone-sensitive lipase are dephosphorylated by protein phosphatase-1, 2A and 2C but not by protein phosphatase-2B

The activity of hormone-sensitive lipase, the rate-limiting enzyme in adipose tissue lipolysis, is controlled by cAMP-mediated phosphorylation at a specific regulatory phosphorylation site. The lipase is also phosphorylated at a site, termed basal, without any effects on its activity [Str?lfors et al. (1984) Proc. Natl Acad. Sci. USA 81, 3317-3321]. The capacity of protein phosphatase-1, 2A, 2B and 2C to dephosphorylate the lipase, selectively phosphorylated by glycogen synthase kinase-4 and cAMP-dependent protein kinase at the basal and regulatory phosphorylation sites, was compared with that towards glycogen phosphorylase and phosphorylase kinase (alpha subunit). Protein phosphatase-1, 2A and 2C were found to dephosphorylate both phosphorylation sites of hormone-sensitive lipase, while protein phosphatase-2B had no measureable activity towards any of the sites. When the activities of protein phosphatase-1, 2A and 2C were normalized with respect to the reference substrates, they were found to dephosphorylate the lipase regulatory site in the approximate relations of 1:4:3 and the basal site in the approximate relations of 1:6:4. Protein phosphatase-1 showed 20% higher and protein phosphatase-2A and 2C 80% higher activity towards the basal site compared to the regulatory site. The two phosphorylation sites of the lipase were comparable to good substrates for protein phosphatase-2A and 2C, but relatively poor substrates for protein phosphatase-1. Protein phosphatase-2C activity towards the lipase was completely dependent on Mg2+ with a half-maximal effect at 3 mM. Protamine increased the lipase dephosphorylation by protein phosphatase-1 3-5-fold with half-maximal effect at 0.6 microgram/ml, and by protein phosphatase-2A about 2-fold with half-maximal effect at 3-5 micrograms/ml, thus illustrating the potential for control of these lipase phosphatase activities.     

A multisubstrate Ca2+ and cyclic nucleotide independent kinase from vascular smooth muscle: modulation of activity by polycations

A multisubstrate Ca2+ and cyclic nucleotide independent kinase (Mr = 47,000) was purified from bovine aortic smooth muscle. Phosphorylation of glycogen synthase by this enzyme was polycation modulable. Low concentrations of polylysine (0.04-0.16 microM) stimulated phosphorylation 2-7 fold, whereas higher concentrations suppressed phosphorylation. Glycogen synthase converted to its glucose 6-PO4 dependent form following phosphorylation in either the presence (7 mol 32P/mol synthase) or absence (4 mol 32P/mol synthase) of polylysine: extent of conversion correlated to extent of phosphorylation. Seven of 14 potential substrates tested were phosphorylated: kinase activity was greatest for phosvitin followed by casein, the receptor protein from type 2 cAMP-kinase, histone H2b, phosphorylase kinase, glycogen synthase, and myocardial myosin light chains. Phosphorylation of phosvitin or synthase was inhibited by heparin (1/2 maximally by 0.5 microgram/ml without salt and 37 micrograms/ml with 150 mM NaCl). The results suggest that the enzyme may participate in regulating arterial glycogen metabolism and that such regulation may be modulated by polycationic and polyanionic effectors.