scholarly journals The role of adenosine 3′:5′-cyclic monophosphate in the regulation of insulin release. Properties of islet-cell adenosine 3′:5′-cyclic monophosphate phosphodiesterase

1972 ◽  
Vol 129 (4) ◽  
pp. 945-952 ◽  
Author(s):  
D. J. Sams ◽  
W. Montague
Keyword(s):  
Cyclic Amp ◽  
Insulin Release ◽  
Islets Of Langerhans ◽  
Gel Filtration ◽  
Apparent Molecular Weight ◽  
Supernatant Fraction ◽  
Phosphodiesterase Activity ◽  
Ph Optimum ◽  
Cyclic Monophosphate ◽  
Km Value

1. An assay has been developed with sufficient sensitivity for determination of the adenosine 3′:5′-cyclic monophosphate diesterase activity in islets of Langerhans, and has been used to investigate the response of the enzyme to various agents which are known to affect insulin release. 2. The subcellular distribution of the enzyme in islets of Langerhans prepared from guinea-pig pancreas was investigated and over 70% of the activity present in the original homogenate was recovered in the supernatant fraction. 3. Gel filtration of the activity present in the supernatant fraction on Sephadex G-200 gave a single peak of activity with an apparent molecular weight of 200000. The phosphodiesterase activity in the peak fraction showed two apparent Km values for adenosine 3′:5′-cyclic monophosphate (cyclic AMP) of 3μm and 30μm, suggesting the presence of two activities. The pH optimum of the activity with the low Km value was 8.7. 4. Theophylline, caffeine, 3-isobutyl-1-methylxanthine (SC-2964), glibenclamide, tolbutamide, xylitol and leucine were inhibitors of the activity with the low Km value; imidazole and arginine stimulated the activity, and glucose and diazoxide were without significant effect. 5. It is suggested that the agents theophylline, caffeine, SC-2964, glibenclamide, tolbutamide, leucine and imidazole may alter the intracellular concentration of cyclic AMP in islets of Langerhans by affecting the cyclic AMP phosphodiesterase activity in islet cells and in this way may affect insulin release.

scholarly journals Characterization of an adenosine 3′:5′-cyclic monophosphate phosphodiesterase from baker's yeast. Its binding to subcellular particles, catalytic properties and gel-filtration behaviour

1977 ◽  
Vol 163 (3) ◽  
pp. 467-476 ◽  
Author(s):  
J Londesborough
Keyword(s):  
Ionic Strength ◽  
Cyclic Amp ◽  
Microsomal Fraction ◽  
Gel Filtration ◽  
Potassium Phosphate ◽  
Apparent Molecular Weight ◽  
Baker’S Yeast ◽  
Baker's Yeast ◽  
Ph Optimum

1. The 3′:5′-cyclic AMP phosphodiesterase in the microsomal fraction of baker's yeast is highly specific for cyclic AMP, and not inhibited by cyclic GMP, cyclic IMP or cyclic UMP. Catalytic activity is abolished by 30 micrometer-EDTA. At 30 degrees C and pH8.1, the Km is 0.17 micrometer, and theophylline is a simple competitive inhibitor with Ki 0.7 micrometer. The pH optimum is about 7.8 at 0.25 micrometer-cyclic AMP, so that over the physiological range of pH in yeast the activity changes in the opposite direction to that of adenylate cyclase [PH optimum about 6.2; Londesborough & Nurminen (1972) Acta Chem. Scand. 26, 3396-3398].2. At pH 7.2, dissociation of the enzyme from dilute microsomal suspensions increased with ionic strength and was almost complete at 0.3 M-KCl. MgCl2 caused more dissociation than did KCl or NaCl at the same ionic strength, but at low KCl concentrations binding required small amounts of free bivalent metal ions. In 0.1 M-KCl the binding decreased between pH 4.7 and 9.3. At pH 7.2 the binding was independent of temperature between 5 and 20 degrees C. These observations suggest that the binding is electrostatic rather than hydrophobic. 3. The proportion of bound activity increased with the concentration of the microsomal fraction, and at 22 mg of protein/ml and pH 7.2 was 70% at I0.18, and 35% at I0.26. Presumably a substantial amount of the enzyme is particle-bound in vivo. 4. At 5 degrees C in 10 mM-potassium phosphate, pH 7.2, the apparent molecular weight of KCl-solubilized enzyme decreased with enzyme concentration from about 200 000 to 40 000. In the presence of 0.5M-KCl, a constant mol.wt. of about 55 000 was observed over a 20-fold range of enzyme concentrations.

scholarly journals The role of adenosine 3′:5′-cyclic monophosphate in the regulation of insulin release by isolated rat islets of Langerhans

1971 ◽  
Vol 122 (1) ◽  
pp. 115-120 ◽  
Author(s):  
W. Montague ◽  
J. R. Cook
Keyword(s):  
Cyclic Amp ◽  
Insulin Release ◽  
Islets Of Langerhans ◽  
Islet Cells ◽  
Intracellular Concentration ◽  
Release Process ◽  
Cyclic Monophosphate ◽  
Extracellular Glucose ◽  
Rat Islets Of Langerhans ◽  
Effect Of Glucose

1. Concentrations of cyclic AMP (adenosine 3′:5′-cyclic monophosphate) and rates of insulin release were measured in islets of Langerhans isolated from rat pancreas and incubated for various times in the presence of glucose, 3-isobutyl-1-methylxanthine, caffeine, theophylline, adrenaline and diazoxide. 2. Caffeine and theophylline produced small but significant increases in both cyclic AMP and release of insulin when they were incubated in the presence of 10mm-glucose. 3. 3-Isobutyl-1-methylxanthine produced a marked increase in the intracellular concentration of cyclic AMP in the presence of 5mm- and 10mm-glucose. However, insulin release was stimulated only in the presence of 10mm-glucose. 4. In response to rising concentrations of extracellular glucose (5–20mm) there was no detectable increase in the intracellular concentration of cyclic AMP even though there was a marked increase in the rate of insulin release. 5. In response to 10mm-glucose insulin release occurred in two phases and 3-isobutyl-1-methylxanthine potentiated the effect of glucose on both phases. The intracellular concentration of cyclic AMP remained constant with glucose and rose within 10min to its maximum value with 3-isobutyl-1-methylxanthine. 6. Adrenaline and diazoxide inhibited insulin release and lowered the intracellular concentration of cyclic AMP when islets were incubated with glucose or 3-isobutyl-1-methylxanthine. 7. It is suggested that glucose does not stimulate insulin release by increasing the concentration of cyclic AMP in islet cells. However, the concentration of cyclic AMP in islet cells may modulate the effect of glucose on the release process.

scholarly journals Isolation, characterization and distribution of adenosine 3′:5′-cyclic monophosphate from Pinus radiata

1978 ◽  
Vol 175 (3) ◽  
pp. 931-936 ◽  
Author(s):  
T Wilson ◽  
E Moustafa ◽  
A G C Renwick
Keyword(s):  
Statistical Analysis ◽  
Cyclic Amp ◽  
Pinus Radiata ◽  
Degrees Of Freedom ◽  
Binding Assay ◽  
Gel Filtration ◽  
Plant Tissues ◽  
Competitive Binding Assay ◽  
Cyclic Monophosphate ◽  
Solvent Systems

Cyclic AMP was extracted in 0.1 M-HCl from tissues of Pinus radiata and purified by gel filtration on Sephadex G-10, and chromatography on Dowex AG1 (X2) and polyethyleneimine-cellulose in two separate solvent systems. Presumptive cyclic AMP from 10kg batches of pine needles was characterized by countercurrent distribution in the presence of cyclic [8-3H]AMP. Statistical analysis of the curves for radioactivity and mass (determined by the Gilman competitive-binding assay) showed that the fit of the curves was highly significant for seven degrees of freedom. The distribution of cyclic AMP within P. radiata and various other plant tissues was determined by the Gilman procedure. The results suggest that there is no relationship between variations in cyclic AMP concentrations and the known function of the tissue in which it was measured.

scholarly journals The mode of action of adenosine 3′:5′-cyclic monophosphate in mammalian islets of Langerhans. Preparation and properties of islet-cell protein phosphokinase

1972 ◽  
Vol 129 (3) ◽  
pp. 551-560 ◽  
Author(s):  
W. Montague ◽  
S. L. Howell
Keyword(s):  
Cyclic Amp ◽  
Islets Of Langerhans ◽  
Islet Cell ◽  
Association Constant ◽  
Cell Protein ◽  
Cyclic Monophosphate ◽  
Endogenous Protein ◽  
Dependent Protein ◽  
Protein Components ◽  
Independent Protein

1. A protein was demonstrated in mammalian islets of Langerhans that after purification appeared as a single component possessing both cyclic-AMP (adenosine 3′:5′-cyclic monophosphate)-binding and cyclic-AMP-dependent protein phosphokinase activities. 2. The protein had an intrinsic association constant for cyclic AMP of 1.15×10−8m, which was similar to the Km for cyclic AMP (1.11×10−8m) of the protein phosphokinase activity. 3. Incubation of the protein in the presence of cyclic AMP resulted in its dissociation into cyclic-AMP-independent protein phosphokinase (catalytic) and cyclic-AMP-binding (receptor) subunits, which could be separated on Sephadex G-200. 4. The cyclic-AMP-dependent protein phosphokinase was capable of phosphorylating a variety of proteins, the most readily phosphorylated being histone, casein and protein components of sub-cellular fractions prepared from islets of Langerhans. 5. The cyclic-AMP-dependent phosphorylation of histone had a Km for ATP of 1.1×10−5m. 6. The endogenous protein phosphokinase activity in rat islets incubated with agents that are known to alter the intracellular concentration of cyclic AMP was investigated. Theophylline and 3-isobutyl-1-methylxanthine, agents that raise cyclic AMP concentrations in islets, increased the activity of the protein phosphokinase, whereas adrenaline, which lowers islet cyclic AMP concentrations, decreased its activity. 7. It is suggested that cyclic AMP may exert its effects on insulin release by increasing the activity of a protein phosphokinase and may thereby promote the phosphorylation and activity of a rate-determining component of the secretory mechanism.

scholarly journals Cathepsin D from pig myometrium. Characterization of the proteinase

1984 ◽  
Vol 219 (3) ◽  
pp. 899-904 ◽  
Author(s):  
R Barth ◽  
E G Afting
Keyword(s):  
Cathepsin D ◽  
Polyacrylamide Gel Electrophoresis ◽  
Sodium Dodecyl ◽  
Gel Filtration ◽  
Polyacrylamide Gel ◽  
Ph Optimum ◽  
Equilibrium Studies ◽  
Main Band ◽  
Km Value ◽  
Ph Range

The purification of cathepsin D from pig uterus by two-step affinity chromatography on concanavalin A- and pepstatin-Sepharose was described previously [Afting & Becker (1981) Biochem. J. 197, 519-522]. In this paper, chemical and physical properties of the proteinase are presented. The purified enzyme showed three bands on SDS (sodium dodecyl sulphate)/polyacrylamide-gel electrophoresis, one main band corresponding to an Mr of 31 000 and two minor bands with Mr values of 43 000 and 15 000 respectively. Gel filtration on Bio-gel P-150 and sedimentation-diffusion equilibrium studies give an Mr for the main band of about 35 000. The pI of the enzyme was determined to be 7.2. Haemoglobin was the best substrate, with a Km value of 6.4 X 10(-6)M. It was hydrolysed with a pH optimum between 3.0 and 3.3 for a substrate concentration of 100 microM. The proteinase was stable over the pH range of 3.5-6.5. At pH 6 the enzyme showed stability up to a temperature of 50 degrees C; at pH 3 the activity was already decreased below 40 degrees C. Carbohydrate studies resulted in the staining of all three bands on an SDS/polyacrylamide gel by thymol/H2SO4. After treatment with endo-beta-N-acetylglucosaminidase H, all three bands were shifted to a region of lower Mr. Of various inhibitors tested, only pepstatin was strongly inhibiting, with a Ki of 2.1 X 10(-9)M.

scholarly journals Ovarian adenosine 3′:5′-cyclic monophosphate-dependent protein kinase(s). Regulation by choriogonadotropin and lutropin in rat ovarian cells

1976 ◽  
Vol 158 (2) ◽  
pp. 175-182 ◽  
Author(s):  
M R Clark ◽  
S Azhar ◽  
K M J Menon
Keyword(s):  
Protein Kinase ◽  
Cyclic Amp ◽  
Kinase Activity ◽  
Activity Ratio ◽  
Gel Filtration ◽  
Supernatant Fraction ◽  
Protein Kinase Activity ◽  
Dependent Protein Kinase ◽  
Ovarian Cells ◽  
Dependent Protein

Choriogonadotropin and lutropin have been found to activate cyclic AMP-dependent protein kinase in ovarian cells isolated by collagenase dispersion from immature rats. The stimulatory effect of gonadotropins was dependent on both hormone concentration and incubation time. Choriogonadotropin at 1 mug/ml fully stimulated the protein kinase activity within 5 min of incubation, and this effect was specific for choriogonadotropin and lutropin-like activity. In addition, protein kinase activity has been characterized with respect to salt sensitivity, cyclic AMP binding, and its responsiveness to gonadotropins and other peptide hormones. Ovarian protein kinase was susceptible to high salt concentrations. The addition of 0.3-1.0 M-NaCl in incubation medium increased the activity ratio with a concomitant decrease in cycle AMP-dependence. The salt effect on protein kinase was observed both from hormone-treated and untreated cells. The hormone-stimulated and unstimulated protein kinase activity was completely stable in the absence of NaCl. No change in the activity ratio was observed when cellular extracts were assayed for protein kinase activity either immediately or after 2 h in the absence of added salt. Gel filtration in the absence of NaCl of cellular extracts prepared from choriogonadotropin-treated and untreated cells showned only a single peak of protein kinase activity that was sensitive to exogenously added cyclic AMP. By contrast, when 0.5 M-NaCl was included in the column buffer, the chromatography of untreated extract showed two peaks of protein kinase activity. The first peak was sensitive to added cyclic AMP, whereas the second peak was insensitive to it. Under identical experimental conditions, protein kinase from gonadotropin-treated cells showed, on gel filtration, only one peak of activity that was totally insensitive to added cyclic AMP. DEAE-cellulose column chromatography of a 20000 g supernatant fraction resulted in a peak of kinase activity that eluted in approx. 0.15 M-NaCl, similar to the similar to the elution of type II protein kinases as described by Corbin et al. (1975) (J. Biol. Chem. 250, 218-225). Choriogonadotropin stimulation produced a decrease in the capacity of protein kinase to bind exogenous cyclic [3H]AMP, with a concomitant increase in the kinase activity ratio. These results are consistent with the notion that cyclic AMP, GENERATED IN SITU Under hormonal stimulation, binds tot he regulatory subunit of protein kinase with subsequent dissociation of the active catalytic subunit from the holoenzyme.

scholarly journals Substrates for cyclic AMP-dependent protein kinase in islets of Langerhans. Studies with forskolin and catalytic subunit

1985 ◽  
Vol 227 (3) ◽  
pp. 727-736 ◽  
Author(s):  
M R Christie ◽  
S J Ashcroft
Keyword(s):  
Protein Kinase ◽  
Cyclic Amp ◽  
Insulin Release ◽  
Islets Of Langerhans ◽  
Plasma Membranes ◽  
Sodium Dodecyl ◽  
Catalytic Subunit ◽  
Subcellular Fractions ◽  
Dependent Protein Kinase ◽  
Dependent Protein

To investigate substrates for cyclic AMP-dependent protein kinase in intact islets of Langerhans, batches of islets were incubated with [32P]Pi for 1 h in the presence of 10 mM-glucose; the adenylate cyclase activator forskolin, which in parallel experiments was shown to increase islet cyclic AMP content and insulin release, was then added. Islets were homogenized and subcellular fractions prepared by differential centrifugation. Phosphopeptides were electrophoresed on sodium dodecyl sulphate/polyacrylamide gels and quantified by autoradiography and densitometry. Within 5 min forskolin caused increased labelling of Mr-25 000 and −30 000 cytosolic and Mr-23 000 and −32 000 particulate peptides; a rapid decrease in phosphorylation of Mr-18 000 and −34 000 cytosolic peptides was also observed. In addition, rather slower phosphorylation occurred of the Mr-15 000 peptide previously identified as histone H3 [Christie & Ashcroft (1984) Biochem. J. 218, 87-99]. When similar subcellular fractions were incubated with [gamma-32P]ATP and purified catalytic subunit of cyclic AMP-dependent protein kinase, peptides phosphorylated included cytosolic species of Mr 25 000 and 30 000 and particulate species of Mr 23 000 and 32 000. The distribution of RNA in the subcellular fractions suggested that the Mr-32 000 species could be a ribosomal protein. The 24 000 g pellet was heterogeneous, as judged by marker assays, and was therefore fractionated further by Percoll-density-gradient centrifugation. The peak containing the Mr-23 000 peptide was resolved from marker enzymes for plasma membranes, mitochondria and endoplasmic reticulum and coincided with a peak for insulin: hence the Mr-23 000 peptide is likely to be a secretory-granule component. The study demonstrates that the potentiation of insulin release that occurs when islet cyclic AMP is increased is accompanied by rapid phosphorylation of specific islet substrates for cyclic AMP-dependent protein kinase. The data are consistent with the hypothesis that protein phosphorylation is involved in the regulation of insulin secretion.

scholarly journals Factors affecting the activity and stability of the palmitoyl-coenzyme A hydrolase of rat brain

1979 ◽  
Vol 179 (3) ◽  
pp. 515-523 ◽  
Author(s):  
Thomas E. Knauer
Keyword(s):  
Molecular Weight ◽  
Rat Brain ◽  
Gel Filtration ◽  
Lower Molecular Weight ◽  
Supernatant Fraction ◽  
Ph Optimum ◽  
Factors Affecting ◽  
Chain Acyl ◽  
Coa Thioesters ◽  
Molecular Weight Form

Palmitoyl-CoA hydrolase (EC 3.1.2.2) catalyses the irreversible hydrolysis of long-chain acyl-CoA thioesters. This enzyme is found primarily in the postmicrosomal supernatant fraction prepared from homogenates of rat brain. Either of two forms of the hydrolase, a lower-molecular-weight species of approx. 70000 or a higher-molecular-weight species of approx. 130000 can be isolated by gel filtration. The higher-molecular-weight form is obtained from columns of Sephadex G-200 eluted with buffer containing 10μm-palmitoyl-CoA or 20% (v/v) glycerol, whereas the lower-molecular-weight form is obtained when the eluting buffer does not contain palmitoyl-CoA or glycerol. The two forms of the hydrolase have the same pH optimum of 7.5, are equally sensitive to the thiol-blocking reagents p-hydroxymercuribenzoate, HgCl2, and 5,5′-dithiobis-(2-nitrobenzoic acid), and exhibit the same Km (1.8μm) with palmitoyl-CoA as substrate. The two forms differ in the availability or reactivity of certain external thiol groups, as determined by covalent chromatography with activated thiol Sepharose. Dilute solutions of the lower-molecular-weight form of the hydrolase rapidly lose activity (50% in 60min at 0°C), but there is no change in the Km with palmitoyl-CoA as substrate during this progressive inactivation. Dilutions of the hydrolase in buffer containing 10μm-palmitoyl-CoA retain full activity. However, addition of palmitoyl-CoA to solutions of the lower-molecular-weight form will not restore previously lost hydrolase activity. The evidence supports the conclusion that the substrate palmitoyl-CoA promotes the formation of a relatively stable dimer from two unstable subunits. This process may not be reversible, since the removal of palmitoyl-CoA or glycerol from solutions of the higher-molecular-weight form does not result in the appearance of the lower-molecular-weight form of the hydrolase.

scholarly journals Purification and properties of a mouse liver plasma-membrane glycoprotein hydrolysing nucleotide pyrophosphate and phosphodiester bonds

1973 ◽  
Vol 135 (4) ◽  
pp. 819-826 ◽  
Author(s):  
W. Howard Evans ◽  
Diana O. Hood ◽  
James W. Gurd
Keyword(s):  
Plasma Membrane ◽  
Mouse Liver ◽  
Gel Filtration ◽  
Apparent Molecular Weight ◽  
Protein Band ◽  
Phosphodiesterase Activity ◽  
Liver Plasma Membrane ◽  
Purification And Properties ◽  
Nucleotide Pyrophosphatase ◽  
Neutral Sugars

1. A mouse liver plasma-membrane preparation was solubilized in an N-dodecylsarcosinate–Tris buffer, pH7.8, and the proteins and glycoproteins were separated by a rate-zonal centrifugation in sucrose–detergent gradients. 2. A peak of alkaline phosphodiesterase activity which sedimented ahead of the 5′-nucleotidase peak was associated with a major glycoprotein component of the plasma membrane. 3. The phosphodiesterase activity was then purified further by gel filtration and gave a single glycoprotein band after electrophoresis on polyacrylamide gels. The apparent molecular weight of the polypeptide at pH7.4 and 8.9 was 128000–130000 and was independent of the polyacrylamide concentration. Electrophoresis in gels containing deoxycholate showed that the protein band was coincident with phosphodiesterase activity. 4. After two-dimensional immunoelectrophoresis, with agarose containing rabbit anti-(mouse plasma-membrane) antiserum as second dimension, the enzyme showed one component which was also coincident with the phosphodiesterase activity. 5. An amino acid composition of the glycoprotein is presented. Carbohydrate analysis indicated the presence of glucosamine, neutral sugars and sialic acid. 6. The enzyme was also a nucleotide pyrophosphatase, as shown by a similar enrichment during purification of activity towards ATP, NAD+, UDP-galactose and UDP-N-acetylglucosamine. The phosphodiesterase activity, measured by using dTMP p-nitrophenyl ester as substrate, was competitively inhibited by nucleotide pyrophosphate substrates. The enzyme showed little or no activity towards RNA, cyclic AMP, AMP, ADP and glycerylphosphorylcholine. 7. The significance of this enzyme activity in the plasma membrane is discussed.

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