Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “PHOSPHORYLASES”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 541 records · Page 30Linked to original sources
PubMed1981

Activity of phosphorylase in total global ischaemia in the rat heart. A phosphorus-31 nuclear-magnetic-resonance study.

1. The uptake and subsequent phosphorylation of deoxyglucose into perfused rat hearts was monitored by 31P n.m.r. 2. The accumulated deoxyglucose 6-phosphate provided (a) an independent method for measuring cytosolic pH in the normoxic and ischaemic heart tissue and (b) a way of studying the activity of phosphorylase during ischaemia. 3. The cytosolic pH measured from the 31P n.m.r. resonance position of deoxyglucose 6-phosphate is in good agreement under all conditions studied with that obtained previously from the Pi resonances. This eliminates any possible doubts about the use of Pi for measuring intracellular pH. 4. Deoxyglucose 6-phosphate in vitro inhibits phosphorylase b but not phosphorylase a. Its inhibitory effect on glycogenolysis during ischaemia is monitored by measuring tissue acidosis by n.m.r. In the initial stages of ischaemia phosphorylase activity is not inhibited, whereas after about 5 min approx. 50% of the activity is inhibited. These observations are interpreted in terms of the relative contributions of phosphorylase a and the AMP-dependent phosphorylase b activities during ischaemia.

Animals↗
PubMed1990

Effect of denervation on the expression of glycogen phosphorylase in mouse skeletal muscle.

After sciatectomy of the left hind-limb of C57BL/J mice, a denervation-induced muscular atrophy ensued and was accompanied by a decrease in the specific activity of glycogen phosphorylase to approx. 25% of control values. The cofactor of phosphorylase, pyridoxal 5'-phosphate, was used as a specific label in the determination of the degradation rate of the enzyme following nerve section. After a delay of 3-4 days, phosphorylase was degraded approx, twice as rapidly in the denervated gastrocnemius (0.20 day-1) as in the control muscle (0.12 day-1). The effect of denervation on phosphorylase mRNA was measured by quantitative Northern-blot analysis using a rat skeletal-muscle phosphorylase cDNA probe. After an initial rapid decline, phosphorylase mRNA levels stabilized in denervated muscle at 50% of the value measured in the contralateral control muscle.

Animals↗
PubMed1997

Antisense inhibition of cytosolic phosphorylase in potato plants (Solanum tuberosum L.) affects tuber sprouting and flower formation with only little impact on carbohydrate metabolism.

To determine the function of cytosolic phosphorylase (Pho2; EC 2.4.1.1), transgenic potato plants were created in which the expression of the enzyme was inhibited by introducing a chimeric gene containing part of the coding region for cytosolic phosphorylase linked in antisense orientation to the 35S CaMV promotor. As revealed by Northern blot analysis and native polyacrylamide gel electrophoresis, the expression of cytosolic phosphorylase was strongly inhibited in both leaves and tubers of the transgenic plants. The transgenic plants propagated from stem cuttings were morphologically indiscernible from the wild-type. However, sprouting of the transgenic potato tubers was significantly altered: compared with the wild-type, transgenic tubers produced 2.4 to 8.1 times more sprouts. When cultivated in the greenhouse, transgenic seed tubers produced two to three times more shoots than the wild-type. Inflorescences appeared earlier in the resulting plants. Many of the transgenic plants flowered two or three times successively. Transgenic plants derived from seed tubers formed 1.6 to 2.4 times as many tubers per plant as untransformed controls. The size and dry matter content of the individual tubers was not noticeably altered. Tuber yield was significantly higher in the transgenic plants. As revealed by carbohydrate determination of freshly harvested and stored tubers, starch and sucrose pools were not noticeably affected by the antisense inhibition of cytosolic phosphorylase; however, glucose and fructose levels were markedly reduced after prolonged storage. These results favour the view that cytosolic phosphorylase does not participate in starch degradation. The possible links between the reduced levels of cytosolic phosphorylase and the observed changes with respect to sprouting and flowering are discussed.

Agrobacterium tumefaciens↗
PubMed1992

The effects of fasting and refeeding on liver glycogen synthase and phosphorylase in obese and lean mice.

The responses of hepatic glycogen synthase and phosphorylase to fasting and refeeding were assessed as part of an investigation into possible sites of insulin resistance in gold thioglucose (GTG) obese mice. The active forms glycogen synthase and phosphorylase (synthase I and phosphorylase a) and the total activity of these enzymes were estimated in lean and GTG mice over 48 h of food deprivation, and for 120 min after glucose gavage (1 g/kg wt). In lean mice there was a maximal reduction in hepatic glycogen content after 12 h of starvation and the activity of phosphorylase a decreased from 23.8 +/- 1.9 to 6.8 +/- 0.7 mumol/g protein/min. These changes were accompanied by an increase in the activity of synthase I (from 0.14 +/- 0.01 to 0.46 +/- 0.04 mumol/g protein/min). In obese mice, similar changes in enzyme activity occurred after 48 h of starvation. These changes were accompanied by a significant reduction in the hyperinsulinemia and hyperglycemia of the GTG mice. After glucose gavage in both lean and obese mice, the activity of synthase I further increased over the first 30 min and declined thereafter. The activity of phosphorylase a increased progressively after refeeding. Results from this study suggest that despite increased hepatic glycogen deposition, the responses of glycogen synthase and phosphorylase, in livers of obese mice, to fasting and refeeding are similar to those of control mice even in the presence of insulin resistance.

Animals↗
PubMed1996

Overexpression of muscle glycogen phosphorylase in cultured human muscle fibers causes increased glucose consumption and nonoxidative disposal.

The effect of increased expression of glycogen phosphorylase on glucose metabolism in human muscle was examined in primary cultured fibers transduced with recombinant adenovirus AdCMV-MGP encoding muscle glycogen phosphorylase. Increments of 20-fold in total enzyme activity and of 14-fold of the active form of the enzyme were associated with a 30% reduction in basal glycogen levels. Total glycogen synthase activity was doubled in AdCMV-MGP-transduced cells even though the activity ratio was decreased. Incubation with forskolin, which inactivated glycogen synthase and activated glycogen phosphorylase, induced greater net glycogenolysis in engineered cells. In unstimulated fibers, lactate production was three times higher in AdCMV-MGP fibers as compared with controls, despite similar rates of glycogenolysis. In transduced fibers incubated with 2-deoxyglucose, the level of 2-deoxyglucose 6-phosphate was about 8-fold elevated over the control even though hexokinase activity was unmodified in AdCMV-MGP fibers. Overexpression of glycogen phosphorylase also led to enhancement of [U-14C]glucose incorporation into glycogen, lactate, and lipid. Accordingly, determination of lipid cell content revealed that engineered cells were accumulating lipids. Furthermore, 14CO2 formation from [U-14C]glucose was 1.6-fold higher, whereas 14CO2 formation from [6-14C]glucose was unmodified, in AdCMV-MGP fibers. Our data show that in human skeletal muscle cells in culture, the increase in glycogen phosphorylase activity is able to up-regulate glycogen synthase activity indicating the enhancement of glycogen turnover. We suggest that the increase in glycogen phosphorylase and, thereby, in glycogen metabolism, is sufficient to enhance glucose uptake in the muscle cell. Glucose taken up by engineered muscle cells is essentially disposed of through nonoxidative metabolism and converted into lactate and lipid.

Carbon Radioisotopes↗
PubMed2001

An inhibitory segment of the catalytic subunit of phosphorylase kinase does not act as a pseudosubstrate.

The C terminus of the catalytic gamma subunit of phosphorylase kinase contains two autoinhibitory calmodulin binding domains designated PhK13 and PhK5. These peptides inhibit truncated gamma(1-300). Previous data show that PhK13 (residues 302-326) is a competitive inhibitor with respect to phosphorylase b, with a K(i) of 1.8 microm. This result suggests that PhK13 may bind to the active site of truncated gamma(1-300). Variants of PhK13 were prepared to localize the determinants for interaction with the catalytic fragment gamma(1-300). PhK13-1, containing residues 302-312, was found to be a competitive inhibitor with respect to phosphorylase b with a K(i) of 6.0 microm. PhK13 has been proposed to function as a pseudosubstrate inhibitor with Cys-308 occupying the site that normally accommodates the phosphorylatable serine in phosphorylase b. A PhK13-1 variant, C308S, was synthesized. Kinetic characterization of this peptide reveals that it does not serve as a substrate but is a competitive inhibitor. Additional variants were designed based on previous knowledge of phosphorylase kinase substrate determinants. Variants were analyzed as substrates and as inhibitors for truncated gamma(1-300). Although PhK13-1 does not appear to function as a pseudosubstrate, several specificity determinants employed in the recognition of phosphorylase b as substrate are utilized in the recognition of PhK13-1 as an inhibitor.

Adenosine Triphosphatases↗
PubMed1976

Glycogen phosphorylase activity in biopsy samples and single muscle fibres of musculus quadriceps femoris of man at rest.

Glycogen phosphorylase activity in biopsy samples of the quadriceps muscle of man taken at rest was measured in the direction of glycogen breakdown. The conditions of assay used were pH 6.8 and 35 degrees C. Mean phosphorylase activity per kg fresh muscle in 8 male volunteers was: phosphorylase a - 259 U, and total phosphorylase - 627 U, where 1 U is the production of 1 mumol glucose-1-phosphate/s under the conditions of assay. The mean value of total activity, transposed to the in vivo condition, is sufficient to support a maximum rate of glycogen degradation calculated as glucosyl units utilized per kg fresh muscle, of 627 mumol/s. This is approximately the rate at which glycolysis occurs during a maximum voluntary isometric contraction. The mean ratio of phosphorylase a activity to total activity at rest was 0.40. Estimates of the mean total phosphorylase activity in type I ('slow') muscle fibres isolated from the quadriceps of 9 volunteers ranged from 210-385 U/kg fresh muscle, and in type II ('fast') muscle fibres from 493-934 U/kg fresh muscle. The average ratio of activity in type II fibres compared with that in type I fibres was 2.5.

Adolescent↗
PubMed1977

Increased muscle phosphorylase in rats fed high levels of vitamin B6.

The present study was undertaken to test the hypothesis that muscle phosphorylase may function as a repository for vitamin B6 in the animal. Since a repository would be expected to accumulate surplus material, one would predict that phosphorylase, which contains stoichio-metric amounts or pyridoxal phosphate, would increase in muscle of animals surfeited with the vitamin. Rats were fed a vitamin B6-free diet supplemented with pyridoxine providing levels 10, 1.0 and 0.1 of those recommended by the National Research Council (NRC). At the high intake level, muscle phosphorylase and total muscle vitamin B6 increased steadily and in almost constant ratio for at least 6 weeks, whereas both alanine and aspartate transaminase increased initially, but reached a plateau within 2 weeks. At the intermediate level of pyridoxine intake, muscle phosphorylase also increased, but less rapidly than in rats fed the higher level. When vitamin B6 intake was restricted to 10% of the NRC-recommended level, no increase in phosphorylase concentration occurred during a period of 10 weeks. These results support the hypothesis that muscle phosphorylase acts as a reservoir for vitamin B6 in the animal and provide experimental evidence that muscle enzyme content expands as vitamin is accumulated during high dietary intake.

Animals↗
PubMed2001

Bone sialoprotein, bone morphogenetic protein 6 and thymidine phosphorylase expression in localized human prostatic adenocarcinoma as predictors of clinical outcome: a clinicopathological and immunohistochemical study of 43 cases.

PURPOSE: Skeletal metastases are the hallmark of advanced prostate cancer and recurrence after local surgery is common. Currently to our knowledge no biological markers predict the risk of disease progression in individuals with localized prostate cancer. In a search for predictive markers we evaluated the expression of bone sialoprotein and bone morphogenetic protein 6, 2 bone related proteins, and the angiogenic factor thymidine phosphorylase. MATERIALS AND METHODS: The study population included 43 men who presented with localized prostate cancer treated with radical prostatectomy. Bone sialoprotein, bone morphogenetic protein 6 and thymidine phosphorylase expression was assessed by immunohistochemical testing. Results were analyzed in relation to pathological disease stage, Gleason score and clinical outcome. Clinical followup was 4.3 to 11.4 years after surgery (median 7.9). RESULTS: Disease did not progress in 17 of the 43 cases, while recurrence and/or metastasis developed in the other 26 at a median of 6.5 and 6.9 years, respectively. Bone sialoprotein and bone morphogenetic protein 6 expression detected in 28 (65%) and 29 (67%) of the 43 samples, respectively, was significantly associated (p = 0.0001). Thymidine phosphorylase detected in 26 samples (60%) was not related to bone sialoprotein and/or bone morphogenetic protein 6 positivity. Bone sialoprotein and/or bone morphogenetic protein 6 expression correlated with bone metastasis, while thymidine phosphorylase expression was related to local recurrence (p = 0.002 and/or 0.007, and 0.00007, respectively). On multivariate analysis only the correlation of thymidine phosphorylase expression with recurrence remained statistically significant (p = 0.002). Co-expression of the 3 markers was observed in the samples of 10 of the 11 patients (90%) with bone metastases and only in 5 of the 17 (29%) who were disease-free. CONCLUSIONS: This study indicates that the expression of bone sialoprotein, bone morphogenetic protein 6 and thymidine phosphorylase determined at a clinically early stage of disease by a simple immunohistochemical technique would enable subgroups of patients to be identified that are at different risks of bone metastasis or recurrence. Detection of such markers would provide additional prognostic information that would be useful for patients with intermediate or low Gleason score or stage disease. These patients would benefit from a more adapted clinical follow-up.

Adenocarcinoma↗
PubMed1996

Glycogen phosphorylase activity during the cold storage of liver: A limiting effect on glycolytic flux and energy production.

This study examined the effects of dibutyryl-cyclic adenosine monophosphate (db-cAMP) and okadaic acid (a specific inhibitor of protein phosphatases 1 and 2A) as additives to a cold storage solution. The effects on levels of glycogen phosphorylase, the resultant effects on flux through the glycolytic pathway, and the consequences of these changes on adenylate (ATP, ADP, and AMP) levels in rat liver during a 24-hr period of cold hypoxia were studied. The rapid transition to anaerobic metabolism was reflected in the increases in lactate levels for all groups. Total lactate accumulation in control livers (flushed and stored with a histidine-lactobionate-raffinose solution) was 9.8 micromol/g. The one notable difference between the control and experimental groups was the total lactate increase in one of the groups treated with db-cAMP; lactate accumulation was 16.0 micromol/g. There was a preferential maintenance of ATP that correlated with the increased flux through glycolysis observed with db-cAMP treatment; levels were 0.4-0.6 micromol/g higher than control group values between 2 and 10 hr of storage. In the control group, levels of glycogen phosphorylase in the active 'a' form began to decrease within 1 hr of exposure to cold hypoxic storage. Values dropped from 86% to 78% within the first 1 hr and by 10 hr, % 'a' was 57%. The separate addition of db-cAMP and okadaic acid resulted in a sustained maintenance of phosphorylase % 'a' throughout the entire cold hypoxic storage period; % 'a' values at 10 hr ranged from 75% to 81%. The major finding of this study was the clear and distinct correlation between phosphorylase % 'a' and total lactate accumulation (index of flux through glycolysis). This relationship was statistically significant after only 1 hr of storage, with a correlation coefficient of r=0.52 (P<0.025); however, the correlation became stronger as the time of storage progressed (by 10 hr, r=0.72; P<0.001). According to the relationship established, the maximum theoretical limit for lactate accumulation with 100% phosphorylase 'a' is approximately 30 micromol/g lactate. This finding suggests that glycogen phosphorylase and not necessarily glycogen content is one major determinant in maintaining anaerobic metabolism and energy production during cold liver storage. Hence, previous experiments that investigated the effects of nutritional status and glycogen content on tissue viability after experimental transplantation need to be reassessed.

Adenosine Diphosphate↗
PubMed2000

Thermal denaturation pathway of starch phosphorylase from Corynebacterium callunae: oxyanion binding provides the glue that efficiently stabilizes the dimer structure of the protein.

Starch phosphorylase from Corynebacterium callunae is a dimeric protein in which each mol of 90 kDa subunit contains 1 mol pyridoxal 5'-phosphate as an active-site cofactor. To determine the mechanism by which phosphate or sulfate ions bring about a greater than 500-fold stabilization against irreversible inactivation at elevated temperatures (> or = 50 degrees C), enzyme/oxyanion interactions and their role during thermal denaturation of phosphorylase have been studied. By binding to a protein site distinguishable from the catalytic site with dissociation constants of Ksulfate = 4.5 mM and Kphosphate approximately 16 mM, dianionic oxyanions induce formation of a more compact structure of phosphorylase, manifested by (a) an increase by about 5% in the relative composition of the alpha-helical secondary structure, (b) reduced 1H/2H exchange, and (c) protection of a cofactor fluorescence against quenching by iodide. Irreversible loss of enzyme activity is triggered by the release into solution of pyridoxal 5'-phosphate, and results from subsequent intermolecular aggregation driven by hydrophobic interactions between phosphorylase subunits that display a temperature-dependent degree of melting of secondary structure. By specifically increasing the stability of the dimer structure of phosphorylase (probably due to tightened intersubunit contacts), phosphate, and sulfate, this indirectly (1) preserves a functional active site up to approximately 50 degrees C, and (2) stabilizes the covalent protein cofactor linkage up to approximately 70 degrees C. The effect on thermostability shows a sigmoidal and saturatable dependence on the concentration of phosphate, with an apparent binding constant at 50 degrees C of approximately 25 mM. The extra stability conferred by oxyanion-ligand binding to starch phosphorylase is expressed as a dramatic shift of the entire denaturation pathway to a approximately 20 degrees C higher value on the temperature scale.

Anions↗
PubMed1991

Elevated thymidine phosphorylase activity in psoriatic lesions accounts for the apparent presence of an epidermal "growth inhibitor," but is not in itself growth inhibitory.

An apparent tissue-specific growth inhibitor, or chalone, obtained from psoriatic lesions was tentatively identified in the 100-kDa fraction based upon inhibition of DNA synthesis, as measured by [3H]-thymidine uptake by a squamous cell carcinoma cell line, SCC 38. This fraction, however, failed to inhibit SCC 38 cell growth when assessed directly in a neutral red uptake assay. Characterization of the inhibitor of [3H]-thymidine uptake revealed it to have biochemical properties identical to thymidine phosphorylase: 1) molecular weight close to 100 kDa, 2) isoelectric point of 4.2, and 3) thymidine phosphorylase enzyme activity. Thus, we conclude that its ability to inhibit [3H]-thymidine uptake was due to thymidine catabolism rather than inhibition of DNA synthesis or growth inhibition. Examination of thymidine phosphorylase activity in keratome biopsies from psoriatic and normal skin demonstrated a twentyfold increase in activity in psoriatic lesions relative to non-lesional or normal skin. This increase in metabolism of thymidine was due to thymidine phosphorylase rather than uridine phosphorylase activity. The correlation between increased thymidine phosphorylase activity and increased keratinocyte proliferation in vitro (cultured) and in vivo (psoriasis), suggests that this enzyme may play a critical role in providing the thymidine necessary for keratinocyte proliferation.

Biopsy↗
PubMed1989

Elevated concentrations of brain-type glycogen phosphorylase in renal cell carcinoma.

We determined tissue concentrations of brain-type glycogen phosphorylase in normal kidney and renal cell carcinoma by enzyme immunoassay; we also localized it immunohistochemically. Tissue concentration of brain-type glycogen phosphorylase in the renal cortex (n = 13) was 1430 +/- 709 ng/mg protein (mean +/- standard deviation) and that in the medulla (n = 13) was 1270 +/- 635 ng/mg protein. On the other hand, the concentration in renal cell carcinoma (n = 26) was 2530 +/- 1540 ng/mg protein, ranging from 520 to 6860 ng/mg, significantly higher than those in renal cortex and medulla. Clear cell type tumors contained slightly higher levels of the phosphorylase (2600 +/- 1430 ng/mg protein) than granular cell type tumors (2100 +/- 1520 ng/mg protein). In renal tissues, brain-type glycogen phosphorylase was immunohistochemically localized in epithelial cells of proximal and distal tubules, collecting tubules, thick and thin limbs of loops of Henle, and Bowman's capsules. In renal cell carcinoma, the phosphorylase was immunohistochemically demonstrated in 97% (34/35) of cases, including one sarcomatoid variant. These findings indicate that renal cell carcinoma cells contain enhanced tissue levels of brain-type glycogen phosphorylase.

Brain↗
PubMed1976

The molecular basis of skeletal muscle phosphorylase kinase deficiency.

The molecular basis of phosphorylase kinase deficiency was investigated in ICR/IAn mice, which show less than 0.2% of normal activity in skeletal muscle (Cohen, P.T.W. and Cohen, P., 1973). The genetics of the deficiency indicate it is a single gene defect on the X-chromosome (Lyon, J.B., 1970). Phosphorylase kinase was purified from skeletal muscle of a control strain, C3H/He-mg, by three different procedures. (a) Ammonium sulphate precipitation and gel filtration on Sepharose 4B. (b) Hydrophobic chromatography and affinity chromatography on Sepharose 4B to which antibody to rabbit muscle phosphorylase kinase has been linked covalently. (c) Precipitation from muscle extracts with anti-phosphorylase kinase antibody. All three procedures showed C3H/He-mg phosphorylase kinases were similar to the rabbit muscle enzymes, the structures of the two isoenzymes being (alphabetagamma)4 and (alpha'betagamma)4 respectively. The proportion of the (alpha'betagamma)4 isoenzyme relative to the (alphabetagamma)4 isoenzyme was however about 1:1 in murine muscle compared to about 1:10 in rabbit muscle. Since the alpha and alpha' subunits appear to be distinct gene products, the defect in ICR/IAn mice cannot be caused by a mutation in the genes coding for either the alpha or alpha'chains, or 50% of normal activity would be observed. All three procedures for C3H/He-mg mice failed to detect any of the four subunits alpha, alpha', beta and gamma in ICR/IAn mice, suggesting that all four chains are absent in the deficiency. An allele for the beta-subunit was identified in rabbits, and the inheritance of the allele showed that it was determined by an autosomal gene. Assuming conservation of X-linkage between mammals, the defect in ICR/IAn mice cannot be caused by a mutation in a beta-subunit gene. It is proposed that ICR/IAn mice are defective in a control gene located on the X-chromosome which is required for the expression of structural genes, at least one of which, the gene for the beta-subunit, is located on an autosome. The results imply that interchromosomal transfer of information takes place during the synthesis of phosphorylase kinase.

Amino Acids↗
PubMed1999

Bacterial alpha-glucan phosphorylases.

Although glycogen and other alpha-1,4-D-glucan storage polysaccharides are present in many bacteria, only few glucan phosphorylases from bacteria have been identified and characterised on the protein or gene level. All bacterial phosphorylases follow the same catalytic mechanisms as their plant and vertebrate counterparts, but differ considerably in terms of their substrate specificity and regulation. The catalytic domains are highly conserved while the regulatory sites are only poorly conserved. The degree of conservation between bacterial and mammalian phosphorylases is comparable to that of other non-mammalian and mammalian alpha-glucan phosphorylases. Only for maltodextrin phosphorylase from E. coli the physiological role of the enzyme in the utilisation of maltodextrins is known in detail; that of all other phosphorylases remains still unclear. Roles in regulation of endogenous glycogen metabolism in periods of starvation, and sporulation, stress response or quick adaptation to changing environments are imaginable.

Bacterial Proteins↗
PubMed1966

Phosphorylase kinase of the liver: deficiency in a girl with increased hepatic glycogen.

Studies of a child with glycogenosis revealed an increased concentration of glycogen and low phosphorylase activity in her liver. Using mixtures of homogenates of the patient's liver and of normal liver, we found the low phosphorylase activity to be caused by a deficiency of phosphorylase kinase and not of hepatic phosphorylase. The fact that phosphorylase activity was restored to normal values by the addition of phosphorylase b kinase from rabbit muscle substantiates this conclusion.

Child, Preschool↗
PubMed1979

Promoter-like mutants with increased expression of the Escherichia coli uridine phosphorylase structural gene.

From an Escherichia coli K-12 strain lacking adenylate cyclase (cya) and cyclic AMP receptor protein (crp), two mutants were isolated that synthesize uridine phosphorylase constitutively. The mutations differ from one another and also from a wild type in the maximum rate of uridine phosphorylase synthesis. They have constitutive expression of the uridine phosphorylase gene (udp) in the presence of repressor protein coded by the cytR regulatory gene and decrease the sensitivity of the udp gene simultaneously with catabolite repression. Both mutations cause a high level of udp expression whether they are in a cya crp or in a cya+ crp+ background. Another mutation (udpP1) isolated previously alters the response of udp gene to the ctyR repressor and produces a higher constitutive level of uridine phosphorylase in a cytR+ than in a cytR background when bacteria are grown in glucose. The synthesis of uridine phosphorylase in this mutant is dependent on an intact cyclic AMP-cyclic AMP receptor protein complex. All mutations studied are cis-acting and extremely closely linked to the udp structural gene, and appear to affect the uridine phosphorylase promoter-operator region. The data obtained are in accordance with a suggestion that the cytR repressor protein normally asserts its function by preventing the positive action of cyclic AMP-cyclic AMP receptor protein complex.

Adenylyl Cyclases↗
PubMed1989

Molecular analysis of GPH1, the gene encoding glycogen phosphorylase in Saccharomyces cerevisiae.

In yeast cells, the activity of glycogen phosphorylase is regulated by cyclic AMP-mediated phosphorylation of the enzyme. We have previously cloned the gene for glycogen phosphorylase (GPH1) in Saccharomyces cerevisiae. To assess the role of glycogen and phosphorylase-catalyzed glycogenolysis in the yeast life cycle, yeast strains lacking a functional GPH1 gene or containing multiple copies of the gene were constructed. GPH1 was found not to be an essential gene in yeast cells. Haploid cells disrupted in GPH1 lacked phosphorylase activity and attained higher levels of intracellular glycogen but otherwise were similar to wild-type cells. Diploid cells homozygous for the disruption were able to sporulate and give rise to viable ascospores. Absence of functional GPH1 did not impair cells from synthesizing and storing trehalose. Increases in phosphorylase activity of 10- to 40-fold were detected in cells carrying multiple copies of GPH1-containing 2 microns plasmid. Northern (RNA) analysis indicated that GPH1 transcription was induced at the late exponential growth phase, almost simultaneous with the onset of intracellular glycogen accumulation. Thus, the low level of glycogen in exponential cells was not primarily maintained through regulating the phosphorylation state of a constitutive amount of phosphorylase. GPH1 did not appear to be under formal glucose repression, since transcriptional induction occurred well in advance of glucose depletion from the medium.

Alleles↗