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PubMed1993

Specific adenosine phosphorylase from hepatopancreas of gastropod Helix pomatia.

1. Specific adenosine phosphorylase from Helix pomatia hepatopancreas was separated from inosine-guanosine phosphorylase and purified 100-165 times; molecular weights were found to be 71,000 and 90,000, respectively. 2. The enzyme is specific for deoxy- and adenosine; it is inactive for 5'-methylthioadenosine and 5-amino-4-imidazole-carboxyamide riboside. Its sensitivity to several inhibitors differs from that of eucaryotic and bacterial purine nucleoside phosphorylases, and is not identical with the sensitivity of the S. mansoni adenosine-splitting enzyme. 3. H. pomatia adenosine phosphorylase differs in its mol. wt and Km values for P(i), ribose 1P, Ado and Ade from adenosine phosphorylase of B. subtilis.

Animals↗
PubMed2006

Bioactivity of glycogen phosphorylase inhibitors that bind to the purine nucleoside site.

The bioactivity in hepatocytes of glycogen phosphorylase inhibitors that bind to the active site, the allosteric activator site and the indole carboxamide site has been described. However, the pharmacological potential of the purine nucleoside inhibitor site has remained unexplored. We report the chemical synthesis and bioactivity in hepatocytes of four new olefin derivatives of flavopiridol (1-4) that bind to the purine site. Flavopiridol and 1-4 counteracted the activation of phosphorylase in hepatocytes caused by AICAR (5-aminoimidazole-4-carboxamide 1-beta-D-ribofuranoside), which is metabolised to an AMP analogue. Unlike an indole carboxamide inhibitor, the analogues 1 and 4 suppressed the basal rate of glycogenolysis in hepatocytes by allosteric inhibition rather than by inactivation of phosphorylase, and accordingly caused negligible stimulation of glycogen synthesis. However, they counteracted the stimulation of glycogenolysis by dibutyryl cAMP by both allosteric inhibition and inactivation of phosphorylase. Cumulatively, the results show key differences between purine site and indole carboxamide site inhibitors in terms of (i) relative roles of dephosphorylation of phosphorylase-a as compared with allosteric inhibition, (ii) counteraction of the efficacy of the inhibitors on glycogenolysis by dibutyryl-cAMP and (iii) stimulation of glycogen synthesis.

Adenosine Monophosphate↗
PubMed2003

Identification of a novel class of inhibitor of human and Escherichia coli thymidine phosphorylase by in silico screening.

Structure-based computational screening of the National Cancer Institute database of anticancer compounds identified novel non-nucleobase-derived inhibitors of human thymidine phosphorylase as candidates for lead optimization. The hierarchical in silico screening strategy predicted potentially strong low molecular weight ligands exhibiting a range of molecular scaffolds. Of the thirteen ligands assayed for activity, all displayed inhibitory activity against Escherichia coli thymidine phosphorylase. One compound, hydrazine carboxamide 2-[(1-methyl-2,5-dioxo-4-pentyl-4-imidazolidinyl)methylene], was found to inhibit E. coli thymidine phosphorylase with an IC(50) value of 20 microM and an IC(50) value of 77 microM against human thymidine phosphorylase. As this hydantoin derivative lacks the undesirable ionic sites of existing tight-binding nucleobase-derived inhibitors, such as 5-chloro-6-[(2-iminopyrrolidin-1-yl)methyl]uracil hydrochloride, it provides an opportunity for the design of potent thymidine phosphorylase inhibitors with improved pharmacokinetic properties.

Binding Sites↗
PubMed2003

Identification of a novel human uridine phosphorylase.

Uridine phosphorylase catalyzes the reversible phosphorylytic cleavage of uridine and deoxyuridine to uracil and ribose- or deoxyribose-1-phosphate. The enzyme has an important role in the metabolism of pyrimidine analogs used in cancer chemotherapy. The cDNA of a novel 317 amino acid human uridine phosphorylase approximately 60% identical to the previously identified human uridine phosphorylase was cloned. The novel enzyme, named uridine phosphorylase-2 (UPase-2), showed broad substrate specificity and accepted uridine, deoxyuridine, and thymidine as well as the two pyrimidine nucleoside analogs 5-fluorouridine and 5-fluoro-2(')-deoxyuridine. The human UPase-2 gene was mapped to chromosome 2q24.1 and the 2.2-kb mRNA was predominantly expressed in kidney. The mouse UPase-2 cDNA was also identified and shown to be predominantly expressed in liver. The identification of a novel uridine phosphorylase with broad substrate specificity is important for studies on both nucleoside metabolism as well as for studies on the pharmacological mechanisms of therapeutic pyrimidine nucleoside analogs.

Amino Acid Sequence↗
PubMed1999

Histochemical mapping of the substrate for brain-stimulation reward with glycogen phosphorylase.

Glycogen phosphorylase is the enzyme that regulates glycogenolysis and it appears that there is a relationship between central levels of glycogen and neuronal activity, which is influenced by a variety of neurotransmitters. In the present study, glycogen phosphorylase histochemistry was used to correlate changes in metabolic activity in response to rewarding lateral hypothalamic stimulation. Rats were allowed to self-stimulate for 1 h per day for ten consecutive days following which postmortem phosphorylase a activity was examined. Significant differences in optical density between the stimulated and contralateral hemispheres were found in three of the eight analyzed structures, two of which, the diagonal band of Broca and the caudate nucleus, showed a greater density of glycogen phosphorylase a on the stimulated side and the third, the habenula, had greater contralateral activity. In conclusion, our data suggest that glycogen phosphorylase activity is a viable but not weighty marker of energy alterations induced by chronic exposure to intracranial self-stimulation, and that it is generally consistent with the patterns revealed by other metabolic indices such as cytochrome oxidase and 2-deoxyglucose autoradiography.

Animals↗
PubMed2003

A theoretical study of effects of cytosolic Ca2+ oscillations on activation of glycogen phosphorylase.

Taking into account the Ca(2+)-stimulated degradation of inositol 1,4,5-trisphosphate (IP(3)) by a 3-kinase, we have theoretically explored the effects of both simple and complex Ca(2+) oscillations on the regulation of a phosphorylation-dephosphorylation cycle process involved in glycogen degradation by glycogen phosphorylase a-form, respectively. For the case of simple Ca(2+) oscillations, the roles of cytosolic Ca(2+) oscillations in the regulation of active phosphorylase depend upon the maximum rate of IP(3) degradation by the 3-kinase, V(M5). In particular, the smaller the values of V(M5) are, the lower the effective Ca(2+) threshold for the activation of glycogen phosphorylase will be. For the case of complex Ca(2+) oscillations, the average level of fraction of active phosphorylase is nearly independent from the level of stimulation increasing in the bursting oscillatory domain. Both simple and complex Ca(2+) oscillations can contribute to increase the efficiency and specificity of cellular signalling, and some theoretical results of activation of glycogen phosphorylase regulated by Ca(2+) oscillations are close to the experimental results for gene expression in lymphocytes.

Calcium Signaling↗
PubMed2001

Fat body fructose-2,6-bisphosphate content and phosphorylase activity correlate with changes in hemolymph glucose concentration during fasting and re-feeding in larval Manduca sexta.

Fasting of second-day fifth instar larval Manduca sexta leads to a rapid decrease in hemolymph glucose concentration from 3.39+/-0.29 to 0.33+/-0.06 mM in 1 h, along with a decrease in the fructose-2,6-bisphosphate content in the fat body (from 5.92+/-0.31 to 2.80+/-0.47 nmol fructose-2,6-bisphosphate/g fat body in 3 h) and activation of fat body glycogen phosphorylase (from 16% to 55-65% phosphorylase a). During re-feeding an increase in the glucose level in the hemolymph was observed (from 0.36+/-0.05 to 3.91+/-0.36 mM in 3 h), along with an increase in the fructose-2,6-bisphosphate level in the fat body (from 2.88+/-0.47 to 6.66+/-0.42 nmol fructose-2,6-bisphosphate/g fat body in 3 h) and inactivation of fat body glycogen phosphorylase (from 56% to 16% phosphorylase a). These data are consistent with the hypothesis that a decrease in hemolymph glucose both activates fat body glycogen phosphorylase and causes a decrease in fat body fructose-2,6-bisphosphate content. Both of these changes would favor conversion of stored glucose to trehalose in the fat body. When second-day larvae were decapitated, the changes in hemolymph glucose and fat body fructose-2,6-bisphosphate were very similar to those observed in fasting whole insects. These data are consistent with a direct role for glucose in controlling carbohydrate metabolism in Manduca sexta.

Animals↗
PubMed1991

Kinetic characterization of the calmodulin-activated catalytic subunit of phosphorylase kinase.

The phosphorylase kinase holoenzyme from skeletal muscle is composed of a catalytic and three different regulatory subunits. Analysis of the kinetic mechanism of the holoenzyme is complicated because both the natural substrate phosphorylase b and also phosphorylase kinase itself have allosteric binding sites for adenine nucleotides. In the case of the kinase, these allosteric sites are not on the catalytic subunit. We have investigated the kinetic mechanism of phosphorylase kinase by using its isolated catalytic gamma-subunit (activated by calmodulin) and an alternative peptide substrate (SDQEKRKQISVRGL) corresponding to the convertible region of phosphorylase b, thus eliminating from our system all known allosteric binding sites for nucleotides. This peptide has been previously employed to study the kinetic mechanism of the kinase holoenzyme before the existence of the allosteric sites on the regulatory subunits was suspected [Tabatabai, L. B., & Graves, D. J. (1978) J. Biol. Chem. 253, 2196-2202]. This peptide was determined to be as good an alternative substrate for the isolated catalytic subunit as it was for the holoenzyme. Initial velocity data indicated a sequential kinetic mechanism with apparent Km's for MgATP and peptide of 0.07 and 0.47 mM, respectively. MgADP used as product inhibitor showed competitive inhibition against MgATP and noncompetitive inhibition against peptide, whereas with phosphopeptide as product inhibitor, the inhibition was competitive against both MgATP and peptide. The initial velocity and product inhibition studies were consistent with a rapid equilibrium random mechanism with one abortive complex, enzyme-MgADP-peptide. The substrate-directed, dead-end inhibitors 5'-adenylyl imidodiphosphate and Asp-peptide, in which the convertible Ser of the alternative peptide substrate was replaced with Asp, were competitive inhibitors toward their like substrates and noncompetitive inhibitors toward their unlike substrates, further supporting a random mechanism, which was also the conclusion from the report cited above that used the holoenzyme.

Amino Acid Sequence↗
PubMed1992

Tracking conformational states in allosteric transitions of phosphorylase.

An intrinsic molecular property of a protein domain can be determined by calculating its principal axes from the inertia tensor matrix. The mass-weighted principal axes can be used to calculate an ellipsoid representing the shape of the protein domain, providing an easy means of visualizing domain movements. Most importantly, the mass-weighted principal axes provide an intuitive means of characterizing domain relationships within a protein, as well as the disposition of domains in different protein conformers. Thus, this method provides a simple, quantitative description of differences of domain positions within various protein structures. We show the utility of this method by characterizing the quaternary and tertiary differences as observed in eight structures of phosphorylated or dephosphorylated glycogen phosphorylase with different effectors bound. This analysis revealed domain movements which were characteristic of the activated phosphorylase structures. The monomers of the phosphorylase dimer were found to move apart by a 2.5-A translation and to rotate apart, in three orthogonal directions, by a minimum of 3.2 degrees. Analysis of the three domains within the phosphorylase monomer showed that both simple and complex domain movements occur and that multiple domain configurations are energetically stable. We suggest that the C-terminal domain of phosphorylase moves along a simple path in the transition from an inactive to active conformation. The direction of translation and rotation is consistent, but the magnitude is variable. In contrast, this analysis showed that the activation domain did not behave as a rigid body, and therefore, the motion of this domain is not as easily characterized.

Allosteric Regulation↗
PubMed1982

Synthesis of 9-(3,4-dioxopentyl)hypoxanthine, the first arginine-directed purine derivative: an irreversible inactivator for purine nucleoside phosphorylase.

The synthesis of two potential arginine-directed purine-based analogues, 6-chloro-9-(3,4-dioxopentyl)purine (6) and 9-(3,4-dioxopentyl)hypoxanthine (7), is reported. Compound 7 was extensively tested as a potential affinity label of purine nucleoside phosphorylase (EC 2.4.2.1) from human erythrocytes. Evidence that 7 reacted with the catalytic center of purine nucleoside phosphorylase includes the following: (1) time-dependent inactivation of the enzyme by 7 was observed; (2) a plot of the pseudo-first-order rate constant for inactivation of the enzyme vs. concentration of 7 was hyperbolic, characteristic of saturation phenomenon; (3) substrates (Pi, arsenate, inosine) and a competitive inhibitor (formycin B) protected the enzyme from inactivation by 7. Compound 7 was 25 times more effective in inhibiting purine nucleoside phosphorylase than butanedione. Evidence that 7 modified arginine(s) includes the following: (1) when the inactivation was performed in borate, both the rate and the extent of inactivation were enhanced compared to those of the controls run in tris(hydroxymethyl)aminomethane hydrochloride (Tris-HCl) buffer; (2) dialysis of inactivator reversed the inactivation in Tris-HCl but not in borate buffer. All the above evidence combined with the previous demonstration [Jordan, F., & Wu, A. (1978) Arch. Biochem. Biophys. 190, 699-704] that butanedione modified only arginines in purine nucleoside phosphorylases and the results presented here demonstrating the similarities in the behavior of butanedione and 7 imply that compound 7 can be called an arginine-directed affinity label for purine nucleoside phosphorylase.

Hypoxanthines↗
PubMed1982

General acid-base catalysis of alpha-glucan phosphorylases: stereospecific glucosyl transfer from D-glucal is a pyridoxal 5'-phosphate and orthophosphate (arsenate) dependent reaction.

D-Glucal, containing a highly reactive double bond, can replace glucose 1-phosphate as the glucosyl donor in phosphorylase-catalyzed glucosyl transfer to a suitable oligo- or polysaccharide acceptor: D-glucal + Pi + (glucose)Pi leads to n 2-deoxy-alpha-D-glucosyl(glucose)n in equilibrium 2-deoxy-alpha-D-glucose-1-P + (glucose)n. This reaction is catalyzed by alpha-glucan phosphorylases from rabbit skeletal muscle, potato tuber, and Escherichia coli. D-Glucal is only measurably consumed by alpha-glucan phosphorylases when orthophosphate or arsenate is present. With saturating concentrations of these anions and a glucosyl acceptor, the D-glucal reaction proceeds at rates comparable with the rates of glucosyl transfer from glucose 1-phosphate and of phosphorolysis or arsenolysis of poly- or oligosaccharides. Furthermore, for the reaction to proceed, the enzyme must be in the active conformation containing the cofactor pyridoxal 5'-phosphate in its dianionic form. On the basis of proton nuclear magnetic resonance spectra, it is proposed that protonation at C-2 of D-glucal gives rise to a hypothetical 2-deoxy-beta-D-glucose intermediate, yielding as a final product (2-deoxy-alpha-D-[2(e)-2H]glucose)n alpha (1 leads to 4) saccharides. These 2-deoxy-alpha-D-glucose oligo- or polysaccharides are degraded by alpha-glucan phosphorylases by phosphorolysis or arsenolysis like natural linear and branched alpha-glucans. The absolute requirement of the D-glucal reaction for phosphate (or arsenate) and its dependency on the dianionic form of the pyridoxal 5'-phosphate bound to phosphorylase are rationalized in terms of a proton transfer relay involving juxtaposed phosphates. Phosphate--phosphate interactions were postulated by Withers et al. [Withers, S. G., Madsen, N. B., Sykes, B. D., Takagi, M., Shimomura, S., & Fukui, T. (1981) J. Biol. Chem. 256, 10759-10762].

Arsenates↗
PubMed1976

The pyridoxal 5' -phosphate site in rabbit skeletal muscle glycogen phosphorylase b: an ultraviolet and 1H and 31P nuclear magnetic resonance spectroscopic study.

1 H NMR spectra of the 3-0-methylpyridoxal 5'-phosphate-n-butylamine reaction product indicated that this analogue forms a Schiff base in aprotic solvent. The uv spectral properties of 3-0-methylpyridoxal-5'-phosphate phosphorylase b correspond to those of the n-butylamine Schiff base derivative in dimethyl sulfoxide. On the basis of that and auxiliary uv and 1H NMR spectra of pyridoxal and pyridoxal 5'-phosphate and the corresponding Schiff base derivatives we have verified that pyridoxal 5' -phosphate is also bound as a Schiff base to phosphorylase and not as an aldamine. Since 3-0-methylpyridoxal-5'-phosphate phosphorylase is active, a proton shuttle between the 3-hydroxyl group and the pyridine nitrogen is excluded. This directs attention to the 5' -phosphate group of the cofactor as a candidate for a catalytic function. 31P NMR spectra of pyridoxal 5' -phosphate in phosphorylase b indicated that deprotonation of the 5' -phosphate group was unresponsive to external pH. Interaction of phosphorylase b with adenosine 5' -monophosphate, the allosteric effector required activity, and arsenate, which substitutes for phosphate as substrate, triggered a conformational change which resulted in deprotonation of the 5' -phosphate group of pyridoxal 5' at pH 7.6. It now behaved like in the pyridoxal-phosphate-epsilon-aminocaproate Schiff base in aqueous buffer, where the diionized form is dominant at this pH. Differences of line widths of the adenosine 5' -monophosphate signal point to different life times of the allosteric effector- enzyme complexes in the presence and absence of substrate (arsenate).

Animals↗
PubMed1975

Amino acid sequence of two functional sites in yeast glycogen phosphorylase.

The structure of two functional sites in baker's yeast (Saccharomyces cerevisiae) glycogen phosphorylase (EC 2.4 1.1) was determined as part of a study on the evolution of regulatory enzymes. S-Carboxymethylated, MaBH4-reduced 32-P-labeled yeast phosphorylase a was cleaved with CNBr, thermolysin, and pepsin. Peptides labeled with 32-P or carrying the fluorescent pyridoxyl marker were isolated and purified using ion-exchange chromatography and gel filtration. CNBr cleavage yielded a single radioactive phosphopeptide (42 residues long) and one small fluorescent peptide with the unique sequence epsilon-Pxy-Lys-Phe-Val-Met. Thermolysin digestion gave rise to one radioactive octapeptide and two fluorescent peptides, 15 and 2 residues long, respectively. From a combination of substractive Edman degradations and digestion with yeast protease C, the sequence of the 32-P-labeled octapeptide was established. Phosphothreonine was identified as the sole phosphorylated amino acid, giving the following structure for the site involved in the covalent regulation of yeast phosphorylase: Leu-Thr(P) -Gly-Phe-Leu-Pro-Gln-Glu. The two fluorescent thermolytic peptides, together with two additional pyridoxyl peptides isolated after peptic digestion of the enzyme yielded the following sequence around the site binding pyridoxal-5'-P, the cofactor essential for phosphorylase activity: Ile-Ser-Thr-Ala-Gly-Thr-Glu-Ala-Ser-Gly-Thr-Ser-Asn-Met-Lys(P Pxy)-Phe-Val-Met. While the phosphorylated site bears no resemblance to the site of covalent control in vertebrate phosphorylases, the pyridoxal-P binding site in the yeast enayme displays remarkable homologies with its animal counterparts; the finding that 14 out of 18 amino acids are identical strongly suggests that the cofactor must be directly involved in catalysis.

Amino Acid Sequence↗
PubMed1998

One-third-the-sites transition-state inhibitors for purine nucleoside phosphorylase.

Genetic defects in human purine nucleoside phosphorylase cause T-cell deficiency as the major phenotype. It has been proposed that efficient inhibitors of the enzyme might intervene in disorders of T-cell function. Compounds with features of the transition-state structure of purine nucleoside phosphorylase were synthesized and tested as inhibitors. The transition-state structure for purine nucleoside phosphorylase is characterized by (1) an elevated pKa at N7 of the purine ring for protonation or favorable H-bond interaction with the enzyme and (2) oxocarbenium ion formation in the ribosyl ring (Kline, P. C., and Schramm, V. L. (1995) Biochemistry 34, 1153-1162). Both features have been incorporated into the stable transition-state analogues, (1S)-1-(9-deazahypoxanthin-9-yl)-1,4-dideoxy-1,4-imino-D-ribitol (immucillin-H) and (1S)-1-(9-deazaguanin-9-yl)-1,4-dideoxy-1, 4-imino-D-ribitol (immucillin-G). Both inhibitors exhibit slow-onset tight-binding inhibition of calf spleen and human erythrocyte purine nucleoside phosphorylase. The inhibitors exhibit equilibrium dissociation constants (Ki) from 23 to 72 pM and are the most powerful inhibitors reported for the enzyme. Complete inhibition of the homotrimeric enzyme occurs at one mole of inhibitor per mole of enzymic trimer. Binding of the transition-state inhibitor at one site per trimer prevents inhibitor binding at the remaining two sites of the homotrimer. A mechanism of sequential catalysis at each subunit, similar to that of F1 ATPase, is supported by these results. Slow inhibitor dissociation (e.g., t1/2 of 4.8 h) suggests that these compounds will have favorable pharmacologic properties. Interaction of transition-state inhibitors with purine nucleoside phosphorylase is different from reactant-state (substrate and product analogue) inhibitors of the enzyme which bind equally to all subunits of the homotrimer.

Animals↗
PubMedDate not supplied

Convergent and divergent evolution of regulatory sites in eukaryotic phosphorylases.

The activity of many proteins in eukaryotic cells is regulated by reversible covalent phosphorylation. This regulatory modification is often linked to other allosteric controls within the same protein, and such overlapping regulatory mechanisms are best characterized for glycogen phosphorylase (EC 2.4.1.1). Phosphorylases from different organisms or cell types exhibit markedly contrasting regulatory features; this makes the enzyme attractive for studying the evolution of interacting molecular regulatory mechanisms. Extensive biochemical and crystallographic studies of rabbit muscle phosphorylase have led to a characterization of five regulatory regions (phosphorylation, glycogen storage, AMP, glucose and purine sites). Here we report the complete primary structure of the yeast Saccharomyces cerevisiae glycogen phosphorylase, deduced from the sequence of the cloned gene. Regions that are highly conserved between muscle and yeast enzymes include the active site, the glycogen storage site and possibly the glucose and purine inhibition sites. Partial conservation of the residues involved in AMP-binding suggests a binding site for the yeast enzyme inhibitor, glucose 6-phosphate. Other parts of the AMP site and the intersubunit contacts involved in AMP allostery are disrupted in the yeast enzyme by extreme sequence divergence. The poor alignment of amino termini and lack of homology at phosphorylation sites indicate that regulation by reversible phosphorylation evolved independently in yeast and vertebrate phosphorylases.

Allosteric Regulation↗
PubMed1976

Glycogen phosphorylase, glucose output and vasoconstriction in the perfused rat liver. Concentration-dependence of actions of adrenaline, vasopressin and angiotensin II.

1. Glycogen phosphorylase (a form, in rapidly freeze-clamped samples) and glucose release were measured in the perfused liver, in response to a range of concentrations of adrenaline, [8-arginine]vasopressin (anti-diuretic hormone) and angiotensin II. 2. All three hormones increased phosphorylase a activity by about 10 mumol/min per g of fresh liver, which was more than sufficient to explain concomitant glucose release (1-2mumol/min per g). 3. Minimally effective concentrations which activated phosphorylase were: adrenaline, 10nM (2ng/ml); vasopressin, 40pM (40pg/ml, 15 muunits/ml); angiotensin II, 60pM (60pg/ml). 4. Glycogen synthase activity was inhibited by adrenaline and vasopressin but not significantly by angiotensin II. 5. Vasoconstriction observed with adrenaline and angiotensin II (but not vasopressin) might explain part of the activation of phosphorylase, since equivalent vasoconstriction (in separate perfusions) activated phosphorylase, did not stimulate glucose output or inhibit synthase. 6. The potency of these effects suggests that all three hormones can stimulate hepatic glycogen degradation in vivo (by direct hepatic action). It is proposed that hormones, and ischaemia, stimulate glycogen degradation to provide glucose phosphates for disposal within the liver cell, as well as for release as free gluose.

Angiotensin II↗
PubMed1980

Glycogen-storage disease in rats, a genetically determined deficiency of liver phosphorylase kinase.

Rats from an inbred strain (NZR/Mh) were found to have high concentrations of glycogen in their livers, even after 24 h of starvation. Despite this, blood glucose concentrations were well maintained on starvation for up to 72 h. The primary defect is a deficiency of liver phosphorylase kinase, causing a lack of active glycogen phosphorylase, although total phosphorylase is normal. The intravenous injection of glucagon caused a rapid activation of cyclic AMP-dependent protein kinase in the liver, but no increase in either phosphorylase kinase or phosphorylase a activity. Although total glycogen synthase activity in the livers of affected rats was higher than normal, glycogen synthase in the active form was very low, presumably as a result of the high liver glycogen content. The condition is transmitted as autosomal recessive and, apart from hepatomegaly, the affected rats appear healthy.

Animals↗
PubMed1980

Phosphorylase kinase phosphorylation of skeletal-muscle troponin T.

Rabbit skeletal-muscle troponin T was phosphorylated by a standard preparation of phosphorylase kinase [Cohen (1973) Eur. J. Biochem. 34, 1--14] and by fractions obtained after chromatography of phosphorylase kinase on phosphocellulose. The original preparation of phosphorylase kinase phosphorylated at least two sites, one of which was serine-1. The second and probably the third sites were presumably located in the peptide flanked by amino-acid residues 147 and 161 of troponin T. Fractions of phosphorylase kinase was adsorbed on phosphocellulose phosphorylated only the second site. Tightly adsorbed fractions possessed high troponin T kinase and phosvitin kinase activities and phosphorylated only serine-1 of troponin T. The results suggest that standard preparations of phosphorylase kinase are contaminated by troponin T kinase, which can phosphorylate serine-1 of troponin T.

Amino Acids↗