Identification and characterization of ribosomal proteins phosphorylated in vaccinia-virus-infected HeLa cells

Two-dimensional analysis of 32P-labelled ribosomal proteins revealed three proteins which are phosphorylated in vaccinia-virus-infected HeLa cells. All three proteins belong to the 40-S ribosomal subunits and were identified as S2, S6 and S16. The ribosomal protein S6 is phosphorylated also in uninfected HeLa cells. Phosphoserine was detected in all three proteins, phosphothreonine only in the protein S2. Phosphorylation of these ribosomal proteins in infected cells is dependent on the multiplicity of the viral infection and increases during the first six hours of infection. All three proteins are also phosphorylated in virus-infected cells treated with cycloheximide and in cells infected with ultraviolet-irradiated virus. This suggests that the phosphorylation reaction involves a vaccinia virion-associated protein kinase.

The antifertility action of alpha-chlorohydrin: enzyme inhibition by alpha-chlorohydrin phosphate

Preparations of the enzymes glyceraldehyde-3-phosphate dehydrogenase and triosephosphate isomerase are shown to be inhibited by alpha-chlorohydrin phosphate (II) in a competitive and non-competitive manner, respectively. alpha-Chlorohydrin (I), glycidol and epi-chlorohydrin have no inhibitory activities suggesting that their antifertility actions are due to their metabolism in vivo to alpha-chlorohydrin phosphate.

Influence of pH on butylylcholinesterase reaction with organophosphorus inhibitors

The non-covalent enzyme . inhibitor complex dissociation constants and the enzyme phosphorylation rate constants were measured as functions of pH in butyrylcholinesterase (actylcholine acylhydrolase, EC 3.1.1.8) reaction with organophosphorus inhibitors (C2H5O)2P(O)SX, where X = (CH2)3SC2H5 and (CH2)6S+(CH3)C2H5. Two ionizing groups, a basic and an acidic one, were revealed in the overall reaction of the enzyme inhibition within the pH range between 5 and 10.5. In the enzyme phosphorylation step only the acidic group was found, while the basic group appeared in the non-covalent binding step of both the ionic and non-ionic compounds. The results strongly imply the participation of the basic functional group in the conformation transition which affects the ability of butyrylcholinesterase to bind hydrophobic reagents in the acidic pH region.

The structural requirements of glucose for phosphorylation by phosphoglucomutase

During catalysis, the phosphoryl group of phosphoglucomutase (alpha-D-glucose-1,6-bisphosphate:alpha-D-glucose-1-phosphate phosphotransferase, EC 2.7.5.1) is transferred through a nucleophilic displacement reaction to the monophosphate substrates to form the diphosphate. Some non-phosphorylated analogs of glucose have been shown to serve as effective acceptors of the active phosphate albeit at a much reduced rate. Several other analogs exhibit little or no reactivity. The relative reaction rates of the reactive analogs follow the order: thioglucose greater than alpha- or beta-D-glucose greater than D-xylose, greater than L-arabinose greater than myo-inositol. The rate of transfer increased with the increased concentration of glucose or its analogs. The products of the reaction may be acid stable ester phosphate or acid labile glycosyl phosphate as well as inorganic phosphate. S-phosphoryl (hemiacetal) thioglucose was identified as a product of the 1-thioglucose reaction. It was possible to define certain steric requirements for the orientation of the hydroxyl groups in all the reacting sugars. These requirements are limited to 3 hydroxyl groups and pertain to loci or receptors on the active site of the enzyme. These would correspond in topography to carbons 2, 3 and 4 of the glucose molecule in the enzyme substrate complex. These hydroxyl groups should be oriented equatorially and project below, above and below the plane of the pyranose ring for C-2, C-3 and C-4, respectively.

The effects of glucagon, catecholamines, and the calcium ionophore A23187 on the phosphorylation of rat hepatocyte cytosolic proteins

Recent experiments have demonstrated that stimulation of rat hepatocyte alpha-adrenergic receptors alters the activity of enzymes known to be regulated by cycles of phosphorylation and dephosphorylation. These events apparently occur without an increase in the activity of adenosine 3':5'-monophosphate-dependent protein kinase. The present study compared the effects of glucagon and catecholamines on the incorporation of radioactive phosphate into cytosolic proteins obtained from intact rat hepatocytes. Sodium dodecyl sulfate-polyacrylamide slab gel electrophoresis resolved 27 phosphorylated bands in the molecular weight range 220,000 to 29,000. Treatment of the intact hepatocytes with glucagon or cyclic nucleotides increased the phosphorylation of 12 of these bands. Incubation of unlabeled cytoplasmic proteins with the catalytic subunit of protein kinase and [gamma-32P]ATP leads to the phosphorylation of 11 proteins. The molecular weights of these proteins were very similar to those altered by glucagon treatment of intact cells. Stimulation of the alpha-receptor with norepinephrine, epinephrine, or phenylephrine in the presence of 20 micrometer propranolol caused an increase in the phosphorylation of at least 10 of the same 12 phosphorylated bands stimulated by glucagon. The increase in phosphorylation mediated by alpha-receptors was only 50 to 60% of that observed with glucagon and occurred in the absence of any change in the level of adenosone 3':5'-monophosphate. The effects of alpha-receptor stimulation could be completely antagonized by 20 micrometer ergotamine or 20 micrometer phentolamine. Treatment of the cells with the Ca2+ ionophore A23187 in an attempt to mimic alpha-receptor function increased the phosphorylation of 4 of the phosphoproteins altered by glucagon or catecholamines. The effects of the ionophore depended on the presence of extracellular Ca2+ ion and were similar in magnitude to those of catecholamines. It is concluded that alpha-receptor occupation alters the activity of an adenosin 3':5'-monophosphate-independent protein kinase or phosphatase with a specificity similar to those affected by cyclic nucleotides.

Binding of divalent cation to phosphoenzyme of sodium- and potassium-transport adenosine triphosphatase

In order to study the action of the divalent cation which is essential for phosphorylation of sodium- and potassium-transport adenosine triphosphatase, magnesium ion, the normal ligand, was replaced with calcium ion, which had properties diffeerent from those of Mg2+, Mn2+, Fe2+, Co2+, Ni2+, or Zn2+. Phosphorylation of the enzyme from ATP at pH 7.4 in the presence of Na+ and Ca2+ yielded a Ca.phosphoenzyme (60% of the maximal level) with a normal rate of dephosphorylation following a chase with unlabeled Ca.ATP (PK = 0.092S-1 at 0 degrees C). In contrast, after a chase by a chelator, namely ethylenediaminetetraacetic acid, 1,2-cyclohexylenedinitrilotetraacetic acid, or ethylene glycol bis-(beta-aminoethyl ether)N,N'-tetraacetic acid, dephosphorylation slowed within 5 s and half of the initial phosphoenzyme remained with a stability about 5-fold greater than normal. Three states of the phosphoenzyme were distinguished according to their relative sensitivity to ADP or to K+ added during a chase. Normally prepared Mg.phosphoenzyme was sensitive to K+ but not to ADP; Ca.phosphoenzyme was sensitive either to ADP or to K+; and the stabilized phosphoenzyme prepared from Ca.phosphoenzyme by addition of a chelator was sensitive neither to ADP nor to K+ nor to both together. Addition of Ca2+ to the stabilized phosphoenzyme restored the reactivity to that of Ca.phosphoenzyme. Addition of Mg2+ to the stabilized phosphoenzyme changed the reactivity to that of Mg.phosphoenzyme. Therefore, this unreactive, stabilized state of the phosphoenzyme appeared to be a divalent cation-free phosphoenzyme. With respect to sensitivity to ouabain, Ca.phosphoenzyme was as sensitive as Mg.phosphoenzyme but calcium-free phosphoenzyme was much less sensitive. It was concluded that the divalent cation required for phosphorylation normally remains tightly bound to the phosphoenzyme and is required for normal reactivity. Calcium ion was almost unique in dissociating relatively easily from the phosphoenzyme. Strontium ion appeared to act similarly to Ca2+.

Glucagon stimulation of rat hepatic phenylalanine hydroxylase through phosphorylation in vivo

Phenylalanine hydroxylase activities in extracts of livers from rats pretreated with glucagon are higher than in controls. This time-dependent activation is seen when the hydroxylase is assayed in the presence of tetrahydrobiopterin, but not in the presence of 2-amino-4-hydroxy-6,7-dimethyltetrahydropterin. A maximum 4-fold stimulation of hydroxylase activity was correlated with a conversion of the multiple forms of the enzyme to a single form. This form is characterized by an increased extent of phosphorylation compared to the unactivated enzyme. Incorporation of radioactive inorganic phosphate into phenylalanine hydroxylase following administration of glucagon was determined after specific immunoprecipitation of the enzyme from partially purified preparations. Sodium dodecyl sulfate disc gel electrophoresis showed that stimulation of enzyme activity is accompanied by incorporation of 32Pi into the protein to the extent of 0.7 mol/mol of hydroxylase subunit. These results demonstrate the phosphorylation of hepatic phenylalanine hydroxylase in vivo and strongly support the idea that the activity of this enzyme can be hormonally regulated through a phosphorylation mechanism.

Partial characterization of protein kinase-catalyzed phosphorylation of low molecular weight proteins in purified preparations of pigeon heart sarcolemma and sarcoplasmic reticulum

Pigeon heart microsomes contain three minor size protein kinase substrates of minimal molecular weights of 22 000, 15 000, and 11500, as estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. When the microsomes were partially loaded with calcium oxalate and subjected to rate zonal and isopycnic centrifugations in sucrose density gradient columns, the 22 000 and the 15 000 dalton proteins settled in the heaviest fraction, which was composed mainly of vesicles of sarcoplasmic reticular membranes; the 11 500 dalton protein was concentrated in the lightest fractions, which consisted chiefly of vesicles of sarcolemmal origin. During incubation of the membrane fractions with Mg [gamma-32P]ATP significant amounts of 32P were incorporated into all these proteins. Incorporation of 32P into the 15 000 dalton protein was moderately and 32P incorporation into the 22 000 dalton protein was markedly enhanced in the presence of exogenous soluble cyclic AMP-dependent protein kinase and cyclic AMP. The phosphorylation of the three proteins was virtually unaffected by Ca2+ concentrations up to 0.1 mM and by ethyleneglycol-bis-(beta-aminoethyl-ether)-N,N'-tetraacetic acid in the absence of added Ca2+. Phosphorylation of the 22 000 and the 11 500 dalton proteins occurred mainly at serine residues. In the 15 000 dalton protein threonine residues were the main site of endogenous phosphorylation. Nearly equal amounts of [32P]-phosphate were incorporated into threonine and serine residues of this protein, when phosphorylation was supported by exogenous cyclic AMP-dependent protein kinase and cyclic AMP. The 15 000 dalton protein could be removed from its membrane attachment by extraction with an acidic chloroform/methanol mixture. This step opens the way for the purification of this membrane-bound protein kinase substrate.

Antagonistic action between cyclic AMP and estrogen in phosphorylation of mammary tumor nuclear proteins

A new protein kinase-dependent phosphorylation occurs in the nuclei of hormone-dependent, 7,12-dimethylbenz[alpha]anthracene (DMBA)-induced mammary carcinoma following preincubation of tumor slices with cyclic adenosine 3',5'-monophosphate (cAMP). The presence of 17beta-estradiol in the medium inhibits this effect. Both events have been observed in vivo in the nuclei of DMBA-induced tumors. The phosphorylation pattern of nuclei in hormone-independent mammary tumor, DMBA No. 1, however, is not affected by preincubation with either cAMP or estrogen. These findings suggest that the antagonistic effect of cAMP and estrogen in the growth control of mammary tumors is exerted through a specific action on nuclear protein phosphorylation and that these events correlate with the hormone-dependency of the tumors.

Phosphorylation

Two-dimensional polyacrylamide-gel electrophoretic analysis of yeast ribosomal proteins labelled in vivo with 32PO43- revealed that the proteins S2 and S10 of the 40S ribosomal subunit, and the proteins L9, L30, L44 and L45 of the 60S ribosomal subunit, are phosphorylated in vivo. Most of the phosphate groups appeared to be linked to serine residues. Teh number of phosphate groups per molecule of phosphorylated protein species ranged from 0.01 to 0.79. Since most of the phosphorylated ribosomal proteins appear to associate with the pre-ribosomal particles at a very late stage of ribosome assembly, phosphorylation is more likely to play a role in the functioning of the ribosome than in its assembly.

Characterization of the cyclic AMP-dependent protein kinase from rat pancreas, further purification of the catalytic subunit, substrate specificity, effect of the pancreatic heat stable inhibitor

In order to investigate the sequence of events triggered by cyclic AMP and cyclic GMP in exocrine pancreatic cells, the identification of the various protein kinases possibly present in this tissue is of major interest. Further analysis of the two cyclic AMP-dependent protein kinases previously reported [11] suggests that KI is a degraded form of KII. It is therefore likely that a single holoenzyme is present in exocrine cells. In addition no protein kinase, specifically stimulated by cyclic GMP, has been detected in any fraction obtained in the course of purification of the cyclic AMP-dependent protein kinase. A faster and more efficient method than the one previously described [11] allows the purification (5000 times) of the protein kinase catalytic subunit. Analysis of the subunit by sodium dodecyl sulphate polyacrylamide gel electrophoresis indicates a molecular weight of 40 000 +/- 1 000. The enzyme phosphorylates specifically histone H2B (Vm = 236 min(-1), Km = 1.15 10(-5) M) and to a lesser extent H2A, H5 and H1 (Vm = 55--77 min(-1), Km 5--25 10(-5) M). Histones H3 and H4 are not phosphorylated. The effect of the heat stable inhibitor, extracted from rat pancreas, on the phosphorylation of H2B has been investigated. The inhibition is of the non competitive type with respect to ATP. The inhibition at various histone concentrations cannot be described by the Michaelis-Menten equation.

Relationship between glucose phosphorylating activities and erythrocyte age

Glucose phosphorylating activity of human erythrocytes quickly decreases during cell ageing; the electrophoretic pattern suggests that this fast decrease is due mainly to the isozyme II. We have shown that in the young cells only hexokinase I and II are responsible for the glucose phosphorylation, while in the old cells another glucose phosphorylating activity, more evident at high glucose concentration, is also present. The appearance of this activity during cell ageing could be interpreted as a post-translational modification of the native hexokinase.

Comparison of interferon action in interferon resistant and sensitive L1210 cells

Translation inhibition, leu-tRNA aminoacylation and double-stranded RNA and ATP dependent phosphorylation were examined in interferon-treated and control cell-free lysates of leukaemic mouse L 1210 R and L 1210 S cells. No differences were observed between the respective interferon-treated and control cell-free extracts, except for the presence of an enhanced 67K dalton phosphoprotein fraction in interferon-treated L 1210 S cell-free extracts. In non-responding cell-free lysates, the lack of stimulation of a 67K dalton phosphoprotein fraction cannot be explained by the presence of an increased level of some inhibitory activity, such as a phosphatase.

[Several properties of 3':5'-AMP-dependent skeletal muscle protein kinases in normal rats and following physical exertion to fatigue]

Three fractions of rat adenosine-3',5'-monophosphate-dependent protein kinase were isolated, partially purified in buffer concentration gradient at normal state and after long-term physical loading and studied. It is found that first two fractions of protein kinases at normal state and after intensive muscular work have similar activities with and without cAMP, apparent Km values for ATP and total histone and half-maximal stimulation by cyclic AMP, but they differed from the third fraction. There are differences in some kinetic parameters and in the cyclic AMP stimulated activities between protein kinases after physical loading. The data obtained suggest the existence of at least two kinases in rat skeletal muscle. The isoenzymes differ in their activities during fatigue.

Temporal changes in histone acetylation

The incorporation of tritiated acetate was studied in developing and aging rats. Thymus, liver and serum were collected 30 minutes after injection of acetate. The trichloroacetic acid precipitable histone fraction was then extracted from liver and thymus and its radioactivity determined. Serum and cytoplasmic fractions were also counted. Serum activity declined with age. Thymus histone and cytoplasmic fractions showed a cyclic pattern. Acetylation of liver histones showed a straight line decline to a relatively constant level. The decline in acetylation of liver histones is postulated to be due to repression of acetylation processes and is thought to parallel the change of hepatocytes from a diploid to a polyploid state.

Direct phosphorylation of brain tyrosine hydroxylase by cyclic AMP-dependent protein kinase: mechanism of enzyme activation

Tyrosine hydroxylase [tyrosine monooxygenase, L-tyrosine, tetrahydropteridine:oxygen oxidoreductase (3-hydroxylating), EC 1.14.16.2] was highly purified from rat caudate nuclei. When the pure hydroxylase was phosphorylated by incubation with cyclic AMP-dependent protein kinase and [32P]ATP, 32P and tyrosine hydroxylase activity were detected after polyacrylamide gel electrophoresis in a single protein band. After sodium dodecyl sulfate gel electrophoresis, 32P was detected only in a probably active subunit of tyrosine hydroxylase of molecular weight 62,000. Phosphorylation of the hydroxylase increased its activity by 2-fold, and was associated with an increase in Vm without any change in Km for either substrate or cofactor. We propose that the pool of native tyrosine hydroxylase is composed of a mixture of enzyme molecules in both active and probably inactive forms, that the active form is phosphorylated, and that phosphorylation produces an active form of the enzyme at the expense of an inactive one.

Protein kinase activity associated with the surface of guinea pig macrophages

Protein kinase activity has been detected associated with the outer surface of guinea pig peritoneal macrophages. Macrophages incubated with [gamma-32P]ATP incorporated 32P-phosphate into cell-associated proteins. Inorganic phosphate did not compete, nor could inorganic [32P]phosphate substitute as the phosphate donor, demonstrating that transfer of phosphate from ATP to protein is direct and extracellular. The macrophage-associated protein kinase was also shown to phosphorylate added acceptor protein (histone) and to be tightly associated with the cell surface. Thus, a new ectoenzyme, a protein kinase, has been detected in macrophages.

Enzymatic conversion of 5'-phosphate-terminated RNA to 5'-di- and triphosphate-terminated RNA

We have isolated from vaccinia virus cores an enzyme, 5'-phosphate-polyribonucleotide kinase, that in the presence of ATP and Mg2+ catalyzes the conversion of 5'-phosphate and 5'-diphosphate termini of RNA to the 5'-triphosphate species. With the exception of dATP, other nucleoside triphosphates were inactive as phosphate donors; activity with dATP was 10% of that observed with ATP. The purified enzyme did not phosphorylate 5'-hydroxyl- or 5'-monophosphate-terminated polydeoxyribonucleotides, although a variety of 5'- monophosphate-terminated RNA chains were active as phosphate acceptors. By using a coupled system of 5'-phosphate-polyribonucleotide kinase and guanylyltransferase in the presence of ATP, GTP, Mg2+, and S-adenosylmethionine, capping of 5'-P-, 5'-PP-, and 5'-PPP-RNA was demonstrated; in the absence of 5'-phosphate-polyribonucleotide kinase only 5'-PPP-RNA was capped by guanylyltransferase.

The isolation and partial characterization of low-molecular-weight phosphorylated component of the non-histone proteins of mouse nuclei

After labelling of mouse liver nuclei with [gamma-32P]ATP in vitro, 10-20% of the radioactivity incorporated into the saline-soluble nuclear and HAP2 chromatin fractions was located in a low-molecular-weight component (component 10) with pI near 4.5 in urea. By using combinations of ion-exchange chromatography, preparative thin-layer isoelectric focusing and gel filtration, this component was isolated from both nuclear fractions. Recovery from the saline-soluble fraction was poor under conditions that allow endogenous phosphatases to be active. Component 10 was shown to be a phosphoprotein on the basis of enzyme-digestion experiments and the detection of phosphoserine and phosphothreonine. The 32P radioactivity did not appear to be associated with phosphorylated basic amino acids. Its molecular weight was determined by gel chromatography and electrophoresis in sodium dodecyl sulphate/polyacrylamide gels as approx. 10000, and tryptic digestion of the reduced carboxymethylated protein in urea yielded two 32P-labelled peptides. It has not been possible as yet to assign a function to component 10, though its similarity to other low-molecular-weight acidic proteins is discussed.

Depolarizing agents and cyclic nucleotides regulate the phosphorylation of specific neuronal proteins in rat cerebral cortex slices

The regulation of the state of phosphorylation of two specific neuronal proteins, designated protein Ia and protein 1b, has been studied in slices of rat cerebral cortex incubated in vitro. For this purpose, a method was developed that prevents dephosphorylation of these proteins during their extraction. When the slices were incubated in a standard Krebs-Ringer solution, proteins Ia and Ib were present almost entirely in the dephosphorylated form. Incubation with cyclic AMP, 8-bromo cyclic AMP, N6-monobutyryl cyclic AMP, or with a phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine, increased the phosphorylation of proteins Ia and Ib in the slices. Depolarization of neuronal membranes by high K+ or by veratridine was also associated with an increased phosphorylation of proteins Ia and Ib. The effect of depolarizing agents, but not that of cyclic nucleotides or 3-isobutyl-1-methylxanthine, required the presence of external Ca2+ in the incubation medium. Tetrodotoxin blocked the stimulation of the phosphorylation of proteins Ia and Ib induced by veratridine but not that induced by the other agents tested. Incubation of the brain slices with 8-bromo cyclic AMP, 3-isobutyl-1-methylxanthine, high K+, or veratridine also increased the state of phosphorylation of two other neuronal proteins found in extracts of the slices.

Evidence that the transforming gene of avian sarcoma virus encodes a protein kinase associated with a phosphoprotein

Avian sarcoma virus (ASV) induces sarcomas in animals and transforms fibroblasts to a neoplastic state in cell culture. A single viral gene (src) is responsible for both the induction and maintenance of neoplastic transformation. Recent work has identified a protein with a molecular weight of 60,000 daltons that is apparently encoded in src and may be the effector molecule for the gene (Brugge and Erikson, 1977; Purchio et al, 1978). The putative product of src can be immunoprecipitated by antisera obtained from rabbits bearing tumors induced by ASV. We have used this approach to isolate the protein to characterize further its genetic origins and possible function. Our rabbit tumor antisera precipitated a protein with a molecular weight of 60,000 daltons; according to serological, biochemical and genetic criteria, this protein is encoded in src. We found that this protein is phosphorylated and therefore denoted it pp60. Phosphorylation of pp60 could be accomplished in vitro with extracts of ASV-infected cells. A temperature-sensitive conditional mutation in src had no demonstrable effect on either the production or stability of pp60 in the infected cell, but phosphorylation of the protein was temperature-sensitive. Since the mutant src is not expressed at the restrictive temperature, our findings raise the possibility that phosphorylation of pp60 is required for its function as the putative effector of src. Immunoprecipitates prepared with extracts of ASV-infected cells and the rabbit tumor antisera contained a protein kinase activity that catalyzed phosphorylation of the heavy chains of immunoglobulin molecules, using either ATP or GTP as phosphate donor. The kinase activity immunoprecipitated in parallel with pp60 was obtained only from cells that contained a functioning product of src and could not be precipitated with antisera directed against structural proteins of ASV. A temperature-sensitive conditional mutation in src caused the kinase activity to be thermally inactivated in vitro far more rapidly than the activity from cells infected with wild-type virus. We conclude that both the protein kinase and pp60 are encoded in src, and that the enzymatic activity may be an intrinsic property of pp60. Phosphorylation of pp60 in cellular extracts was inhibited by calcium ion, whereas the immunoprecipitable kinase activity was not, suggesting that the kinase responsible for pp60 phosphorylation may be distinct from that encoded in src. Collett and Erikson (1978) have also identified a protein kinase activity associated with pp60. These findings raise the possibility that phosphorylation of specific cellular targets might account for transformation of the host cell by src.

Effects of adenosine 3' : 5'-monophosphate and guanosine 3' : 5'-monophosphate on calcium uptake and phosphorylation in membrane fractions of vascular smooth muscle

The effects of adenosine 3' : 5'-monophosphate (cyclic AMP), guanosine 3' : 5'-monophosphate (cyclic GMP) and exogenous protein kinase on Ca uptake and membrane phosphorylation were studied in subcellular fractions of vascular smooth muscle from rabbit aorta. Two functionally distinct fractions were separated on a continuous sucrose gradient: a light fraction enriched in endoplasmic reticulum (fraction E) and a heavier fraction containing mainly plasma membranes (fraction P). While cyclic AMP and cyclic GMP had no effect on Ca uptake in the absence of oxalate, both cyclic nucleotides inhibited the rate of oxalate-activated Ca uptake when used at concentrations higher than 10(-5) M. The addition of bovine heart protein kinase to either fraction produced an increase in the rate of oxalate-activated Ca uptake which was further augmented by cyclic AMP. Cyclic GMP caused smaller stimulations of protein kinase-catalyzed Ca uptake than cyclic AMP. Mg-dependent phosphorylation, attributable to endogenous protein kinase(s), was inhibited in fraction E by low concentrations (10(-8) M) of both cyclic AMP and cyclic GMP. In fraction P, an inhibition by cyclic AMP occurred also at a concentration of 10(-8) M, while with cyclic AMP a concentration of 10(-5) M was required for a similar inhibition. Bovine heart protein kinase stimulated the phosphorylation of the membrane fractions much more than Ca uptake. In fraction E, in the presence of bovine protein kinase, both cyclic AMP and cyclic GMP stimulated phosphorylation up to 200%. Under these conditions, no stimulation was observed in fraction P. These results are compatible with the hypothesis that in vascular smooth muscle soluble rather than particulate protein kinases are involved in the regulation of intracellular Ca concentration.

Isolation of tau-phosphohistidine from a phosphoryl-enzyme intermediate of human prostatic acid phosphatase

The carbethoxylation of prostatic acid phosphatase (orthophosphoric-monoester phosphohydrolase (acid optimum), EC 3.1.3.2) was accompanied by modification of histidine residues and the inactivation of the enzyme. These findings are consistent with photoinactivation experiments described earlier (Rybarska, J. and Ostrowski, W (1974) Acta Biochim, Polon. 21, 377--390). Prostatic acid phosphatase was phosphorylated at alkaline pH using p-nitrophenyl [32P]phosphate as substrate. Phosphoryl enzyme is stable in alkaline solutions and undergoes dephosphorylation at acidic pH. After hydrolysis of phosphoryl enzyme in strong alkaline solution, a single phosphoryl amino acid was isolated from hydrolyzate and identified as the tau-phosphohistidine.

Studies of fluoride-preactivated rabbit liver adenylyl cyclase

Rabbit liver adenylyl (ATP pyrophosphate-lyase (cyclizing), EC 4.6.1.1) cyclase was stimulated by preincubation with F- and Mg2+ and the stimulation persisted despite extensive washing and/or detergent solubilization. Optimum preactivation conditions were found to be 4 mM NaF and 2 mM MgCl2; higher or lower concentrations produced submaximum stimulation regardless of preincub ation time. In addition to an enhanced catalytic acticity, the activated enzyme also exhibited different responses to Ca2+ and Cu2+ when compared to the basal enzyme. ATP caused a time-dependent inhibition that could be partially prevented or reversed by F-, but was not completely reversed by washing. This inhibition was not observed when 5'-adenosine(beta, gamma-imide) triphosphate blocks inhibition by ATP. The results support, but do not prove, the proposed molecular basis of F- activation which entails a phosphorylation-dephosphorylation mechanism.

Phosphorylation of chromatin- and ribosome-associated proteins in cells transformed by adenovirus, murine sarcoma virus, and methylcholanthrene

Endogenous protein phosphorylation in chromatin and ribosomes of monkey, mouse, and rat cells transformed by DNA, RNA tumor viruses, and a chemical carcinogen revealed the association of a protein of approximately 90,000 daltons (90K), which is highly phosphorylated in vitro. Peptide map analysis showed that the 90K proteins associated with these organelles of various transformed cells are similar irrespective of the species of cells and transforming agents. This species of protein could not be detected, or was scarcely detected, by phosphorylation in chromatin and ribosomes of untransformed cells and in revertants of transformed cells. These results suggest that the alteration in the pattern of endogenous protein phosphorylation in these organelles is closely related to the transformed state of cells.

Dephosphorylation of histones H1 and H3 during the isolation of metaphase chromosomes

Histones have been extracted from isolated metaphase chromosomes prepared by the method of Wray and Sutbblefield [Exp. Cell Res 59, 469-478 (1970)] and by a Nonidet P-40 detergent procedure based on the method of Wigler and Axel [Nucleic Acids Res. 3, 1463-1471 (1976)]. Analysis of the densitometer profiles of long polyacrylamide gels shows that the mitotic phosphorylations of histone H1 (H1M) and histone H3 are extensively depleted during chromosome isolation. These data indicate that CHO metaphase chromosomes prepared by standard methodologies do not represent in vivo chromosomes with respect to their histone phosphorylations; therefore, current chemical and structural studies of isolated metaphase chromosomes may require further clarification.

Analysis of phosphorylation of protein synthesis initiation factor eIF-2 by two-dimensional gel electrophoresis

We describe a method for examining the state of phosphorylation of initiation factor eIF-2 in reticulocyte lysates. The procedure involves incubation of the lysate with iodo[1-14C]acetate in 8.5 M urea, and fractionation of the labelled proteins by two-dimensional acrylamide gel electrophoresis. This approach has been used to show that haem deficiency, double-stranded RNA, and oxidised glutathione, which all inhibit the initiation of protein synthesis in an analogous manner, all cause a net increase in the level of phosphorylated eIF-2 in the complete lysate protein synthesis system.

Jejunal phosphorylation and dephosphorylation of absorbed pyridoxine.HCl in vitro

The phosphorylation and dephosphorylation of absorbed vitamin was studied in rat jejunal everted sacs during in vitro uptake of [3H]pyridoxine.HCl. Kinetic studies during 4-min incubations demonstrated that phosphorylation was saturable (Km, 13.3 micron; Vmax, 0.906 nmol/4 min/g wet tissue) and was significantly inhibited by both structural and metabolic inhibitors. Longer incubations (30-min) demonstrated similar saturation and inhibition of net phosphorylation. Dephosphorylation of the phosphate esters formed by the phosphorylation step also occurred, as demonstrated by pulse-chase experiments. Disappearance of these phosphates was initially rapid, approximated first order kinetics, and apparently was mediated by a phosphatase. Whereas phosphorylation did not appear to affect initial uptake rates for [3H]pyridoxine.HCl by the jejunum, net phosphorylation after more prolonged incubations qualitatively paralleled accumulation of total absorbed vitamin in tissue over the same time. The primary effect of phosphorylation during jejunal uptake of pyridoxine by rat jejunum was to increase the accumulation of absorbed pyridoxine in tissue during prolonged incubations. Dephosphorylation had the net effect of limiting the magnitude of that accumulation.