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T R Soderling

Publications and source records attributed to T R Soderling.

At least 127 records · Page 7Linked to original sources
PubMed1980

Epinephrine regulation of skeletal muscle glycogen metabolism. Studies utilizing the perfused rat hindlimb preparation.

Studies of rat skeletal glycogen metabolism carried out in a perfused hindlimb system indicated that epinephrine activates phosphorylase via the cascade of phosphorylation reactions classically linked to the beta-adrenergic receptor/adenylate cyclase system. The beta blocker propranolol completely blocked the effects of epinephrine on cAMP, cAMP-dependent protein kinase, phosphorylase, and glucose-6-P, whereas the alpha blocker phentolamine was totally ineffective. Omission of glucose from the perfusion medium did not modify the effects of epinephrine. Glycogen synthase activity in control perfused and nonperfused muscle was largely glucose-6-P-dependent (-glucose-6-P/+glucose-6-P activity ratios of 0.1 and 0.2, respectively). Epinephrine perfusion caused a small decrease in the enzyme's activity ratio (0.1 to 0.05) and a large increase in its Ka for glucose-6-P (0.3 to 1.5 mM). This increase in glucose-6-P dependency correlated in time with protein kinase activation and was totally blocked by propranolol and unaffected by phentolamine. Comparison of the kinetics of glycogen synthase in extracts of control and epinephrine-perfused muscle with the kinetics of purified rat skeletal muscle glycogen synthase a phosphorylated to various degrees by cAMP-dependent protein kinase indicated that the enzyme was already substantially phosphorylated in control muscle and that epinephrine treatment caused further phosphorylation of synthase, presumably via cAMP-dependent protein kinase. These data provide a basis for speculation about in vivo regulation of the enzyme.

Animals↗
PubMed1979

Stimulation of glycogen synthase phosphorylation by calcium-dependent regulator protein.

Phosphorylation of skeletal muscle glycogen synthase catalyzed by a protein kinase is stimulated up to 10-fold by the calcium-dependent regulator (CDR) protein. Half-maximal stimulation requires about 1 microgram of CDR/ml. Phosphorylation by the CDR-dependent synthase kinase is more rapid at pH 8.6 than at pH 6.8 and is blocked by ethylene glycol bis(beta-aminoethyl-ether)N,N'-tetraacetic acid and trifuloperazine. Approximately 60 to 70% of the phosphate is incorporated into the trypsin-insensitive region of glycogen synthase resulting in conversion of the a form to the b form of the enzyme. The CDR-dependent synthase kinase is not myosin light chain kinase, as this enzyme does not phosphorylate glycogen synthase. Furthermore, synthase phosphorylation by the cAMP-dependent protein kinase catalytic subunit is not affected by CDR. The possibility that CDR-dependent synthase kinase may be phosphorylase kinase is being investigated.

Animals↗
PubMed1979

Regulatory functions of protein multisite phosphorylation.

In recent years it has become apparent that an increasing number of proteins can be phosphorylated at several different sites. In this article protein multisite phosphorylation is discussed with reference to the enzymes glycogen synthase, pyruvate dehydrogenase, and phosphorylase kinase. Each of these enzymes contains three or more different phosphorylation sites on one or more subunits. Activation and inactivation of the enzymes appear to correlate quite well with phosphorylation of a few key sites on the protein. The other phosphorylation sites may influence other kinetic properties of the enzymes or regulate the rates of dephosphorylation of the key sites by the appropriate phosphatase. Thus, multisite phosphorylation may represent an important mechanism for regulating several functions of complex proteins.

Animals↗
PubMed1979

Phosphorylation and inactivation of glycogen synthase by phosphorylase kinase.

Skeletal muscle glycogen a4-synthase (EC 2.4.1.11) has been purified free of all synthase kinase and phosphatase activities by chromatography on a Glc-N-6-P-Sepharose affinity column and then on a phosphocellulose column. This preparation of glycogen synthase was tested as a substrate for purified skeletal muscle phosphorylase kinase (ATP:phosphorylase-b phosphotransferase, EC 2.7.1.38). Phosphorylase kinase (1-10 microgram/ml or 0.03-0.3 microM) catalyzes rapid phosphorylation of glycogen synthase (4.5 microM) associated with conversion of the active a form to the less active b form. In the reaction, greater than 95% of the 32P incorporation from [gamma-32P]ATP goes into the synthase subunit almost exclusively in the trypsin-insensitive region which is responsible for synthase a-to-b conversion. Synthase phosphorylation or inactivations catalyzed by phosphorylase kinase is blocked by ethylene glycol bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid, is ATP dependent, is 10-fold more rapid at pH 8.6 than at pH 6.8, and is increased 10-fold by prior activation of the phosphorylase kinase with MgATP and cyclic AMP. With activated phosphorylase kinase at pH 8.2 the apparent Km and Vmax are approximately 70 microM and 4 mumol/min per mg with glycogen synthase and 70 microM and 9 mumol/min per mg with phosphorylase as substrate. It is concluded that glycogen synthase is a substrate in vitro for phosphorylase kinase, a Ca2+-dependent enzyme. The possible physiological significance of this reaction is discussed.

Animals↗
PubMed1978

Relationships between dephosphorylation and D to I conversion of rabbit skeletal muscle glycogen synthase.

The relationship between dephosphorylation and D to I conversion of skeletal muscle glycogen synthase by synthase phosphatase was investigated using synthase preparations containing 1 to 3 mol of 32P/mol of subunit (90,000 g). Dephosphorylation was analyzed in terms of 32P release from the trypsin-sensitive and trypsin-insensitive phosphorylation regions of synthase. With synthase containing 1 to 2 mol of 32P/90,000 g, dephosphorylation of the trypsin-insensitive region correlated closely with D to I conversion and was more rapid than dephosphorylation of the trypsin-sensitive region. Synthase containing 3 mol of 32P/90,000 g was a relatively poor substrate for the phosphatase since dephosphorylation of both regions, as well as D to I conversion, was slow. With this species of synthase, glucose-6-P (0.1 mM) increased the rates of D to I conversion and dephosphorylation of trypsin-insensitive region. It is concluded that dephosphorylation of the trypsin-insensitive region is responsible for the conversion of synthase D to I.

Animals↗
PubMed1977

Modulation of protein phosphorylation by a factor purified from adipocytes.

1. A factor which modulates the activity of cyclic AMP-dependent protein kinase copurifies from rat adipocytes with an inhibitor of adenylate cyclase. Purification and stability studies suggest that both effects reside in a single factor previously referred to as a feedback regulator. 2. The magnitude and direction of the feedback regulator effect on cyclic AMP-dependent protein kinase activity was dependent on the concentration of feedback regulator and the concentration and type of protein substrate. Using histone type IIA as substrate, feedback regulator was inhibitory at low histone concentrations and stimulatory at high concentrations. Preincubation of protein kinase with feedback regulator resulted in inhibition at all histone concentrations. With some protein substrates, e.g. histone f2b and casein, inhibition was observed at all histone concentrations. 3. The stimulation of histone type IIA phosphorylation resulted from an increased V with no effect on either the apparent Ka for cyclic AMP or the Km for ATP. Time course studies suggest that feedback regulator increased the rate of phosphorylation without increasing the total number of phosphorylation sites. Increased histone phosphorylation was observed regardless of whether the cyclic AMP-dependent protein kinase was peak I or peak II (off Deae-cellulose), isolated from bovine or rabbit skeletal muscle or rat heart. A small stimulation was observed using cyclic GMP-dependent protein kinase. 4. These results indicate that feedback regulator can inhibit or stimulate protein kinase, an effect which is probably substrate directed, and depends on the reaction conditions. Whether feedback regulator modulated protein phosphorylation in vivo in addition to its inhibition of adenylate cyclase is unknown. However, stimulation of protein kinase activity in the presence of cyclic AMP is a valuable and rapid assay for monitoring feedback regulator fractions during purification procedures.

Adipose Tissue↗
PubMed1976

Regulation of glycogen synthetase. Effects of trypsin on the structure, activity, and phosphorylation of the skeletal muscle enzyme.

Incubation of purified skeletal muscle glycogen synthetase I with trypsin (10 mug/ml) for 15 min decreased the Stokes radius of the enzyme from 68 A to 62 A and the subunit molecular weight from 90,000 to about 73,000. No decrease in the sedimentation coefficient of 13.3 S could be detected. It was calculated that native synthetase I is a tetramer of molecular weight 360,000 to 370,000. Trypsin also catalyzed a decrease in the synthetase activity ratio (minus glucose-6-P to plus glucose-6-P) largely by reducing minus glucose-6-P activity. The magnitude of the trypsin effect on the synthetase activity ratio was very similar to that produced by phosphorylation of synthetase by the cyclic AMP-dependent protein kinase. The activity ratio could be lowered from that characteristic of synthetase I, 0.85, to 0.25 either by trypsin digestion or by incorporation of 1 mol of Pi per mol of synthetase subunit. An activity ratio of less than 0.05 could be obtained in three ways as follows, (a) phosphorylation to 2 Pi/subunit, (b) phosphorylation to 1 Pi/subunit (ratio=0.25) followed by trypsin treatment, (c) trypsin treatment (ratio=0.25) followed by phosphorylation. When trypsinized synthetase was phosphorylated by the catalytic subunit of cyclic AMP-dependent protein kinase, 1 Pi/subunit was incorporated. Trypsin (6 mug/ml) led to a rapid release of about 50% of the radioactivity from 32P-synthetase regardless of whether the enzyme contained 1 or 2 phosphates per subunit. It was concluded that two sites on the enzyme subunit are highly susceptible to phosphorylation catalyzed by the cyclic AMP-dependent protein kinase. The data indicate that the 1st mol of Pi incorporated is distributed about equally between the two sites. A model is proposed to account for these observations. The data further indicate that a peptide containing one site is removed by trypsin. This reduces enzyme activity to the same extent as does phosphorylation of the site in the intact protein.

Animals↗
PubMed1975

Regulation of glycogen synthetase. Specificity and stoichiometry of phosphorylation of the skeletal muscle enzyme by cyclic 3':5'-AMP-dependent protein kinase.

Complete conversion of skeletal muscle glycogen synthetase from the I form to the D form requires incorporation of 2 mol of phosphate per enzyme subunit (90,000 g). Incubation of sythetase I with low concentrations of adenosine 3':5'-monophosphate(cAMP)-dependent protein kinase (10 units/ml) and ATP (0.1 to 0.3 mM) plus magnesium acetate (10 mM) results in incorporation within 1/2 hour of 1 mol of phosphate persubunit concomitant with a decrease in the synthetase activity ratio (minus glucose-6-P/plus glucose-6-P) from 0.85 to 0.25. Further incubation for 6 hours does not greatly increase the phosphate content of the synthetase or promote conversion to the D form. This level of phosphorylation is not increased by raising the concentration of protein kinase to 150 units/ml and is not influenced by the presence of glucose-6-P, UDP-glucose, or glycogen. However, at protein kinase concentrations of 10,000 to 30,000 units/ml a second mol of phosphate is incorporated per subunit, and the sythetase activity ratio decreases to 0.05 or less. In addition to the 2 mol of phosphate persubunit which are required for formation of sythetase D, further phosphorylation can be observed which is not associated with changes in synthetase activity. This phosphorylation occurs at a slow rate, is increased by raising the ATP concentration to 2 to 4mM, and is not blocked by the heat-stable protein inhibitor of cAMP-dependent protein kinase. These data indicate that skeletal muscle glycogen synthetase contains multiple phosphorylation sites only two of which are involved in the synthetase I to D conversion.

Adenosine Triphosphate↗
PubMed1975

Hormonal regulation of adenosine 3',5'-monophosphate-dependent protein kinase.

There appear to be two classes of protein kinases in rat heart and adipose tissue, types I and II. Type I elutes from DEAE-cellulose at smaller than 0.1 M NaCl and type II at greater than 0.1 M NaCl. The type I enzyme is more readily dissociated by salt or histone than is the type II enzyme. If the type I kinase is first dissociated by cAMP, the subunits reassociate very slowly at 0 degrees C on removal of the cAMP by Sephadex G-25 chromatography, whereas those of type II reassociate very rapidly. Rat heart contains mostly type I and a small amount of type II enzyme, whereas adipose tissue contains almost exclusively the type II enzyme. The adipose tissue enzyme resembles the heart type II kinase in all of the above properties, although the two enzymes are not identical as indicated by slight differences in elution patterns from DEAE-cellulose columns. Incubation of rat epididymal adipose tissue with low concentrations of epinephrine (0.11 muM) increases glycerol production and the fraction of the protein kinase in the active form (activity ratio). The change in cAMP under these conditions is not statistically significant. The presence of insulin inhibits the epinephrine effect on glycerol production and protein kinase but has no measurable effect on cAMP levels. Incubation of adipose tissue with high epinephrine concentrations (11 muM) increases the cAMP level, the protein kinase activity ratio, and glycerol production. Under these conditions insulin decreases the cAMP level and kinase activity ratio but does not reduce glycerol production. The data suggest that very small changes in the tissue cAMP level, undetectable by the assay method, are magnified during the stepwise activation of glycerol output aided possibly by cooperative effects between cAMP and protein kinase. The procedure developed for determining the state of activation of the cAMP-dependent protein kinase in adipose tissue must be modified by reducing the salt concentration of the buffers in order to carry out similar studies in the heart. This reflects the different types of protein kinase in the two tissues. The addition of charcoal to crude extracts of heart prevents protein kinase activation by added cyclic AMP. Charcoal should therefore prevent any activation that could occur if any sequestered cAMP were released during homogenization. Charcoal addition thereby provides a means to distinguish intracellular cAMP activation of the kinase from that which might occur following cell rupture. If epinephrine-perfused hearts are homogenized in the presence of charcoal, epinephrine stimulation of the protein kinase is only slightly decreased. This indicates that the protein kinase is activated intracellularly by cAMP and suggests that all of the cAMP in the cell is available to the protein kinase; i.e., cAMP is not released during homogenization.

Adipose Tissue↗