Expressions of two types of soluble cAMP-dependent protein kinases of the rabbit myometrium in different functional states

Two types of soluble cAMP-dependent protein kinase (I and II) were isolated from rabbit myometrium cytosol at functional rest and characterized. In pregnancy, protein kinase is represented by type II alone. Upon delivery, one isoform of the enzyme was detected, which was eluted from a DEAE-cellulose column with 0.15-0.22 M. NaCl. During the postnatal period, the elution profile of the enzyme is made up of two protein bands, one fraction being eluted with 0.15-0.22 M NaCl (93% of total enzyme content), and the other one being represented by a minor component eluted with 0.07-0.09 M. NaCl (7%). In terms off isoenzyme activity, main kinetic properties, ability to autophosphorylate and Kass for cAMP, the protein kinase isolated during delivery and the major protein kinase fraction obtained in the postnatal period can be related to protein kinases type II. Quantitative and qualitative expression of two types of soluble cAMP-dependent protein kinase from rabbit myometrium isolated at different functional states may be due to differences in their biological activity.     

Membrane-bound forms of Ca2+-dependent protein modulator: Ca2+-dependent and independent binding of modulator protein to the particulate fraction from brain.

Ca2+-dependent binding of modulator protein to the particulate fraction was studied. The particulate fraction from one gram of rat brain bound in a Ca2+-dependent fashion 144 microgram of modulator protein, representing more than one third of the total soluble modulator protein in this tissue. The binding site was present in both the mitochondrial and microsomal fractions, the specific activity of the microsomes being the higher. The binding was reversible with a physiological concentration of Ca2+, and was temperature-dependent, and the site can be saturated with modulator protein (4.5 microgram modulator protein per mg of microsomal protein). Tryptic digestion of the membranes caused complete disappearance of the binding activity, but heat-treatment for 5 min at 70 degrees C caused only 40% loss of activity. The binding site may be a known or unknown enzyme(s), the activity of which is regulated by Ca2+ and modulator. Alternatively, this binding site may be a nonenzymic protein that regulates the concentration of free modulator protein in the cell.     

DUSP13B/TMDP inhibits stress-activated MAPKs and suppresses AP-1-dependent gene expression

Sulfotransferases catalyze the transfer of sulfate group from para-nitrophenyl sulfate (pNPS) or 3'-phosphoadenosine-5'-phosphosulfate (PAPS) onto acceptor molecules in the biosynthesis of sulfate esters. Human pathogenic mycobacteria are known to produce numerous sulfated molecules on their cell surface which have been implicated as important mediators in host-pathogen interactions. The open reading frame stf9, a predicted homologue of sulfotransferase in the Mycobacterium avium genomic data, was cloned and over expressed in Escherichia coli. The recombinant STF9 conserved the characteristic PAPS binding motif of sulfotransferase and was purified as a 44?kDa soluble protein which exhibited transfer of sulfate group from pNPS (K (m) 1.34?mM, V (max) 7.56?nmol/min/mg) onto 3'-phosphoadenosine-5'-phosphate (K (m) 0.24?mM, V (max) 10.36?nmol/min/mg). The recombinant STF9 protein was also capable of transferring sulfate group from PAPS onto certain acceptor substrates in E. coli, and showed binding affinity to the PAP-agarose resin, supporting the sulfotransferase activity of the recombinant STF9 protein. This is the first report of molecular evidence for sulfotransferase activity of a protein from M. avium. Mutation of Arg96 to Ala and Glu170 to Ala abolishes sulfotransferase activity, indicating the importance of Arg96 and Glu170 in STF9 activity catalysis.     

GALACTOCEREBROSIDE SULFOTRANSFERASE: FURTHER CHARACTERIZATION OF THE ENZYME FROM RAT BRAIN

Abstract— Myelin has an unusual lipid composition, being particularly rich in sulfatide. This lipid is synthesized by the transfer of sulfate from phosphoadenosine phosphosulfate to galactocerebroside, catalyzed by galactocerebroside sulfotransferase. This paper describes a sensitive assay for the sulfotransferase (capable of measuring activity in as little as 10 μg of extracted rat brain protein) so that this enzyme can be readily investigated in isolated cells, or the small amounts of tissue available in developing animals. Both manganase (20 m m ) and thiol reagents were required for optimal activity. This assay was used to monitor the purification of the sulfotransferase from rat brain. Extraction of the enzyme from crude homogenates required the nonionic detergent, Triton X-100, at pH 7–7.5. Removal of Triton X-100 from the extracted enzyme resulted in a soluble but less active enzyme, the activity of which could then be restored with detergents. Stability of the detergent-extracted enzyme was investigated, and even at —40°C there was a 20% loss of activity over 10 days. By standard procedures 500-fold purification of the enzyme has been achieved.     

Effect of electrical stimulation post mortem of bovine muscle on the binding of glycolytic enzymes. Functional and structural implications.

The extent of binding of glycolytic enzymes to the particulate fraction of homogenates was measured in bovine psoas muscle before and after electrical stimulation. In association with an accelerated glycolytic rate on stimulation, there was a significant increase in the binding of certain glycolytic enzymes, the most notable of which were phosphofructokinase, aldolase, glyceraldehyde 3-phosphate dehydrogenase and pyruvate kinase. From the known association of glycolytic enzymes with the I-band of muscle it is proposed that electrical stimulation of anaerobic muscle increases enzyme binding to actin filaments. Calculations of the extent of enzyme binding suggest that significant amounts of enzyme protein, particularly aldolase and glyceraldehyde 3-phosphate dehydrogenase, are associated with the actin filaments. The results also imply that kinetic parameters derived from considerations of the enzyme activity in the soluble state may not have direct application to the situation in the muscle fibre, particularly during accelerated glycolysis.     

Soluble precursor of membrane-associated protein kinase in uterine smooth muscle cells

Incubation of smooth muscle strips from rat uterus with isoproterenol resulted in redistribution of protein kinase activity between the cytosol and a 20,000 to 50,000g membrane fraction. Similarities in the elution properties of the cytosolic and membrane-associated forms of the enzyme on DEAE-cellulose ion exchange chromatography further suggested the two forms were the same. The nature of membrane binding of the soluble enzyme was investigated using smooth muscle microsomal and cytosol fractions. Membranes readily bound the soluble enzyme when the two subcellular compartments were reconstituted and incubated at 30 °C for 10 min. The extent of binding was proportional to the ratio of membranes to cytosol and was characterized by the inhibition of soluble enzyme activity toward exogenous substrates in a Triton X-100 reversible manner. In marked contrast to the binding of soluble protein kinase to heart particulate fractions, binding of the cytosol enzyme to smooth muscle cell membranes was unaffected by ionic strength or cAMP. The latter property indicated holoenzyme was bound in a manner similar to the free catalytic subunit of cAMP-dependent protein kinase and suggested the enzyme was bound by association between the membrane and the catalytic subunit. Binding of cytosol protein kinase to the membranes rendered the enzyme insensitive to trypsin digestion and the capacity of the smooth muscle cell membranes to bind the soluble enzyme exceeded that of other rat tissue fractions. Resistance to salt extraction and proteolysis, as well as its detergent dependence, suggested the soluble enzyme became an integral or intrinsic membrane protein following association with the membrane. The ability of membranes to incorporate [γ-³²P]ATP into phosphoprotein was lost on detergent extraction of protein kinase and restored in an apparently specific manner when extracted and washed membranes were reconstituted with soluble enzyme. The intrinsic nature of membrane protein kinase and the apparent specificity with which the soluble enzyme was hound by membranes further indicated that, in myometrium. hormone-induced translocation of protein kinase is an important mechanism by which enzyme activity is increased in the vicinity of its in situ substrates.     

Purification and identification of the heat-stable factor required for pregnenolone-binding protein activity. Evidence that the factor is adenosine 3',5'-diphosphate.

This paper presents data identifying adenosine 3',5'-diphosphate (3',5'-ADP) as the small heat-stable factor essential for the active steroid binding complex of the adrenocortical pregnenolone-binding protein (PBP). Factor activity obtained from the boiled supernatant of partially purified PBP was isolated by high performance liquid chromatography using weak anion-exchange and hydrophobic (C18) chromatography sequentially. The purified material retained characteristic factor activity and presented a UV spectrum identical to that for authentic 3',5'-ADP. Mass spectroscopic analysis of the isolated factor revealed an M-H ion of appropriate mass (m/z = 426) and a decomposition pattern for the M-H ion that was consistent with the structure of 3',5'-ADP. The studies presented here demonstrate that authentic 3',5'-ADP can categorically substitute for factor prepared from the soluble fraction of the guinea pig adrenal. Specifically, 3',5'-ADP potentiated ligand binding of partially purified native PBP and restored binding capacity to alkaline phosphatase-inactivated PBP in a dose-dependent manner. As is the case for adrenocortical factor activity, these effects were negated by pretreating the 3',5'-ADP with calf intestinal alkaline phosphatase. Other nucleotides similarly tested, including ADP isomers, were ineffective as factor substitutes. The sulfated form of 3',5'-ADP (i.e. 3'-phosphoadenosine 5'-phosphosulfate) demonstrated some potential for restoring binding capacity to phosphatase-inactivated PBP; however, this compound was clearly inhibitory rather than stimulatory for native PBP activity. Taken collectively, the data overwhelmingly demonstrate that 3',5'-ADP is in fact the molecule required by the PBP for high affinity steroid binding complex formation. It is not yet known whether 3',5'-ADP acts allosterically or contributes directly to the structure of the steroid binding site.     

Identification of gastric mucosal mucus glycoprotein sulfotransferase.

Sulfation of mucus glycoproteins, reaction catalyzed by Golgi resident sulfotransferase, is an important event in posttranslational processing of gastric mucins. Here we report the purification of mucus glycoprotein sulfotransferase enzyme from the microsomal fraction of rat gastric mucosa. The enzyme was released from the membrane with 0.5% Triton X-100 and precipitated from the 100,000xg supernatant with 90% ice-cold acetone. The enzyme activity (44.7 pmol/mg/45 min) in the precipitate was enriched nearly 10-fold compared to Triton X-100 extract of microsomal membrane (4.2 pmol/mg/45 min). On SDS-PAGE, the enzyme gave a single 43 kDa protein band, which was active towards mucin, but did not catalyze the sulfation of galactosylceramide. The study is the first to report the characteristics of a sulfotransferase enzyme specific for gastric mucin.     

Adrenocortical pregnenolone-binding protein activity requires a small heat-stable factor: evidence that regulation by phosphorylation/dephosphorylation occurs at the level of the factor, not the protein.

The steroid-binding capacity of the adrenocortical pregnenolone-binding protein (PBP) is effectively destroyed by extreme temperature (boiling water for 2-5 min); however, the boiled preparation contains a factor that potentiates ligand binding when readded to native PBP. Treatment of the boiled fraction with calf intestinal alkaline phosphatase at pH 9 reverses the stimulatory effect on PBP activity. Additionally, if native PBP is first incubated with alkaline phosphatase, which converts it to a nonbinding form, activity can be fully restored in a dose-dependent manner by the addition of the boiled preparation. The factor (itself devoid of binding capacity) can also be generated by exposing native PBP to acidic conditions (pH 4). The molecule is small (mol wt, less than 2000), as judged by Sephadex G-25 gel filtration and equilibrium dialysis. It is not retained on Concanavalin-A-Sepharose and is not extractable with a variety of organic solvents. The factor remains active after lyophilization and has a net negative charge at pH 7.4 (determined by DEAE-cellulose chromatography). While the binding capacity of native PBP is destroyed by a variety of proteases, the heat-stable factor is unaffected by similar treatment. Additionally, factor activity is not susceptible to RNase, DNase, or lipase digestion. Thus, the protein moiety of the PBP has an absolute requirement for a distinct phosphorylated heat-stable factor for expression of ligand-binding activity, and it may be through this factor that binding activity is regulated. It is not yet known whether the factor is acting allosterically or actually functions as part of the steroid-binding site.     

Phytochrome controlled acid RNase: An “attached” protein of ribosomes

The light-dependent increment in RNase activity (which is ribosome bound in cell extracts) is distributed as a gradient increasing from base to hook of lupin hypocotyls. No evidence was found of non-specific or of specific activation of pre-formed enzyme molecules following isolation, either before or after (latent activity) destruction of particles. The autodegradation capacity of ribosomes isolated from irradiated cells was almost double that of ribosomes from etiolated tissue. It is proposed that association between the bulk of the light-controlled RNase fraction and lupin ribosomes results from binding of soluble protein. It is not clear whether binding is specific or an artifact of isolation.     

Comparison of estrogen sulfotransferase and pregnenolone sulfotransferase of guinea pig.

Guinea pig adrenal estrogen sulfotransferase from either sex was eluted as a single peak, irrespective of buffer salt concentration, when subjected to fast protein liquid chromatography on gel filtration columns. The same enzyme was consistently eluted in two distinct peaks during chromatofocusing. Adrenal pregnenolone sulfotransferase was eluted during gel filtration in a heterogeneous pattern, dependent on salt concentration. These properties have made possible almost complete separation of the two sulfotransferases in one step, although adrenal estrogen sulfotransferase may possess a minute intrinsic ability to catalyze sulfation of pregnenolone. Pregnenolone sulfotransferase had no measurable activity toward estrone. Pregnenolone sulfotransferase from both sexes yielded variable elution patterns during chromatofocusing. Estrogen sulfotransferase from the adrenal, as well as that of guinea pig chorion, was strongly inhibited by N-ethylmaleimide and to a lesser degree by iodoacetamide and iodoacetate. Adrenal and chorion estrogen sulfotransferases were thermolabile and were activated, although not protected from the effect of heat, by binding to 3'-phosphoadenosine 5'-phosphosulfate. Adrenal pregnenolone sulfotransferase was inhibited only by high concentrations of N-ethylmaleimide and not at all by iodoacetamide or iodoacetate. It was more thermostable than the estrogen sulfotransferase and was not activated by binding to 3'-phosphoadenosine 5'-phosphosulfate.     

Changes in ATP sulfurylase and adenosine 5'-phosphosulfate sulfotransferase activity during autumnal senescence of beech leaves

The decrease in extractable activity of ribuloscbisphosphate carboxylase (EC 4.1.1.39), ATP sulfurylase (EC 2.7.7.4) and adenosine 5'-phosphosulfate sulfotransferase and the content in chlorophyll and protein was compared in leaves of cloned beech trees ( Fagus sylvatica L.) during autumnal senescence. Leaves excised at the same time but containing different amounts of chlorophyll gave extracts with correspondingly varying amounts of ribulosebisphosphate carboxylase activity. Leaves which had almost completely lost this enzyme activity contained still appreciable ATP sulfurylase and adenosine 5'-phosphosulfate sulfotransferase activity and soluble protein. For all components determined, there was a period lasting until mid or end of October during which there was no or only a small decrease. They were then all lost rapidly from the leaves. The specific activity of ribulosebisphosphate carboxylase decreased during this phase of rapid loss, whereas it remained essentially constant for ATP sulfurylase and adenosine 5'-phosphosulfate sulfotransferase. During this period, the mean half life of ribulosebisphosphate carboxylase was shorter than the one of ATP sulfurylase and of adenosine 5'-phosphosulfate sulfotransferase. These experiments clearly show that ribulosebisphosphate carboxylase was preferentially lost from beech leaves during autumnal senescence as compared to ATP sulfurylase and adenosine 5'-phosphosulfate sulfotransferase.     

The schistosome enzyme that activates oxamniquine has the characteristics of a sulfotransferase

Available evidence suggests that the antischistosomal drug oxamniquine is converted to a reactive ester by a schistosome enzyme that is missing in drug-resistant parasites. This study presents data supporting the idea that the active ester is a sulfate and the activating enzyme is a sulfotransferase. Evidence comes from the fact that the parasite extract loses its activating capability upon dialysis, implying the requirement of some dialyzable cofactor. The addition of the sulfate donor 3'-phosphoadenosine 5'-phosphosulfate (PAPS) restored activity of the dialyzate, a strong indication that a sulfotransferase is probably involved. Classical sulfotransferase substrates like beta-estradiol and quercetin competitively inhibited the activation of oxamniquine. Furthermore, these substrates could be sulfonated in vitro using an extract of sensitive (but not resistant) schistosomes. Gel filtration analysis showed that the activating factor eluted in a fraction corresponding to a molecular mass of about 32 kDa, which is the average size of typical sulfotransferase subunits. Ion exchange and affinity chromatography confirmed the sulfotransferase nature of the enzyme. Putative sulfotransferases present in schistosome databases are being examined for their possible role as oxamniquine activators.     

Trypsin-like enzyme activity of the extracellular membrane vesicles of Bacteroides gingivalis W50

Trypsin-like enzyme activity in spent culture media from 3-d-old batch cultures of Bacteroides gingivalis W50 was measured by using the hydrolysis of N alpha-benzoyl-L-arginine-p-nitroanilide. The cell-free culture medium was fractionated by differential centrifugation at 10,000 g and 75,000 g, yielding two particulate fractions and a soluble supernatant fraction. About 80% of the total recoverable activity was associated with the particulate fractions, the remainder being in the supernatant. Electron microscopy of ruthenium-red/osmium stained ultrathin sections of the pellet fractions showed them to be composed of vesicular particles (extracellular vesicles), between 50 and 250 nm in diameter. Enzyme activity in all three fractions was enhanced by dithiothreitol. Gel-permeation chromatography of the soluble fraction yielded one peak of activity which contained 64 kDa and 58 kDa polypeptides. Enzyme activity from the vesicular fractions could be solubilized by sonication, giving a similar chromatographic profile to the supernatant fraction. The main peak of activity was composed of 64 kDa and 58 kDa polypeptides. In addition, there was a higher molecular mass enzyme activity peak composed of the 64 kDa and 58 kDa components along with 111 kDa, 93 kDa and 70 kDa polypeptides. We conclude that the trypsin-like enzyme of B. gingivalis is released as a soluble protein and is also associated with extracellular vesicles, in which it may exist as a soluble component and also as a protein complex.     

Correlation between PAP-dependent steroid binding activity and substrate specificity of mouse and human estrogen sulfotransferases

Estrogen sulfotransferase (EST) is a cytosolic enzyme that catalyzes the sulfoconjugation and inactivation of estrogens using 3'-phosphoadenosine-5'-phosphosulfate (PAPS) as an activated sulfate donor. A finding of undetermined significance in the study of EST has been that the guinea pig EST is able to bind pregnenolone and estradiol with high affinity in the presence of PAP, the reaction by-product of the sulfate donor PAPS. This finding has raised the possibility that EST may have other physiological functions independent of its enzymatic activity as a sulfotransferase. To determine if the PAP-dependent steroid binding activity is a common property shared by other estrogen sulfotransferases, we have expressed the mouse and human EST in bacteria and used the purified protein to address this question. We found that, in the presence of PAP, both recombinant mouse and human EST were able to bind estradiol with high affinity but only the human EST was able to bind pregnenolone. In addition, we show that human but not the mouse EST was also able to bind dehydroepiandrosterone, a property that was not described for the guinea pig EST. Furthermore, we demonstrate that the promiscuity of human EST in steroid binding is mirrored by a correspondingly low substrate specificity in its enzymatic activity as a sulfotransferase. Reversely, the lack of stable binding of pregnenolone and dehydroepiandrosterone by the mouse EST is paralleled by a lack of sulfotransferase activity of this enzyme toward these two steroids. Mutagenesis of mouse EST within a domain critical for PAPS binding abolished both its sulfotransferase and PAP-dependent estrogen binding activity. These data suggest that stable binding of steroids such as pregnenolone or estrogen is not an independent property of estrogen sulfotransferases but rather is related to their catalytic activity.     

Characterization of the protein kinase activities of human platelet supernatant and particulate fractions.

After human platelets were lysed by freezing and thawing in the presence of EDTA, about 35% of the total cyclic AMP-dependent protein kinase activity was specifically associated with the particulate fraction. In contrast, Ca2+-activated phospholipid-dependent protein kinase was found exclusively in the soluble fraction. Photoaffinity labelling of the regulatory subunits of cyclic AMP-dependent protein kinase with 8-azido-cyclic [32P]AMP indicated that platelet lysate contained a 4-fold excess of 49 000-Da RI subunits over 55 000-Da RII subunits. The RI and RII subunits were found almost entirely in the particulate and soluble fractions respectively. Chromatography of the soluble fraction on DEAE-cellulose demonstrated a single peak of cyclic AMP-dependent activity with the elution characteristics and regulatory subunits characteristic of the type-II enzyme. A major enzyme peak containing Ca2+-activated phospholipid-dependent protein kinase was eluted before the type-II enzyme, but no type-I cyclic AMP-dependent activity was normally observed in the soluble fraction. The particulate cyclic AMP-dependent protein kinase and associated RI subunits were solubilized by buffers containing 0.1 or 0.5% (w/v) Triton X-100, but not by extraction with 0.5 M-NaCl, indicating that this enzyme is firmly membrane-bound, either as an integral membrane protein or via an anchor protein. DEAE-cellulose chromatography of the Triton X-100 extracts demonstrated the presence of both type-I cyclic AMP-dependent holoenzyme and free RI subunits. These results show that platelets contain three main protein kinase activities detectable with histone substrates, namely a membrane-bound type-I cyclic AMP-dependent enzyme, a soluble type-II cyclic AMP-dependent enzyme and Ca2+-activated phospholipid-dependent protein kinase, which was soluble in lysates containing EDTA.     

The effect of soluble rat liver proteins on the activity of microsomal stearoyl-CoA and linoleoyl-CoA desaturase.

1. The influence of bovine serum albumin and soluble rat liver proteins on the activity of rat liver microsomal delta9 and delta6 desaturases has been studied. 2. In the absence of bovine serum albumin, the delta9 desaturase which converts stearoyl-CoA into oleoyl-CoA, shows a non-linear correlation between enzyme activity and protein concentration. 3. Optimum concentrations of bovine serum albumin have three main effects on the enzyme activity: (i) establishes a linear relationship between enzyme activity and protein concentration, (ii) stimulates the enzyme activity 2--3-fold and (iii) raises the optimum substrate concentration from 10 to 100 muM. 4. A highly purified soluble liver protein of molecular weight 24 000 also stimulated the enzyme activity and brought about a linear relationship between enzyme activity and protein concentration. 5. It was concluded that the non-linear kinetics were due to limiting amounts of substrate binding protein in the microsomal preparations. 6. The delta6 desaturase which converts linoleoyl-CoA into gamma-linolenoyl-CoA was also stimulated by bovine serum albumin and soluble liver proteins. 7. The significance of the fatty acid-binding proteins is discussed.     

Degradation of Alzheimer's ß-Amyloid Protein by Human and Rat Brain Peptidases: Involvement of Insulin-Degrading Enzyme

We examined the degradation of Alzheimer's ß-amyloid protein (1–40) by soluble and synaptic membrane fractions from post mortem human and fresh rat brain using HPLC. Most of the activity at neutral pH was in the soluble fraction. The activity was thiol and metal dependent, with a similar inhibition profile to insulin-degrading enzyme. Immunoprecipitation of insulin-degrading enzyme from the human soluble fraction using a monoclonal antibody removed over 85% of the ß-amyloid protein degrading activity. Thus insulin-degrading enzyme is the main soluble ß-amyloid degrading enzyme at neutral pH in human brain. The highest ß-amyloid protein degrading activity in the soluble fractions occurred between pH 4–5, and this activity was inhibited by pepstatin, implicating an aspartyl protease. Synaptic membranes had much lower ß-amyloid protein degrading activity than the soluble fraction. EDTA (2mM) caused over 85% inhibition of the degrading activity but inhibitors of endopeptidases –24.11, –24.15, –24.16, angiotensin converting enzyme, aminopeptidases, and carboxypeptidases had little or no effect.