Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0038187 (starvation)
 24,951 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The phosphorylated form of liver glycogen phosphorylase (alpha-1,4-glucan : orthophosphate alpha-glucosyl-transferase, EC 2.4.1.1) (phosphorylase a) is active and easily measured while the dephosphorylated form (phosphorylase b), in contrast to the muscle enzyme, has been reported to be essentially inactive even in the presence of AMP. We have purified both forms of phosphorylase from rat liver and studied the characteristics of each. Phosphorylase b activity can be measured with our assay conditions. The phosphorylase b we obtained was stimulated by high concentrations of sulfate, and was a substrate for muscle phosphorylase kinase whereas phosphorylase a was inhibited by sulfate, and was a substrate for liver phosphorylase phosphatase. Substrate binding to phosphorylase b was poor (KM glycogen = 2.5 mM, glucose-1-P = 250 mM) compared to phosphorylase a (KM glycogen = 1.8 mM, KM glucose-1-P = 0.7 mM). Liver phosphorylase b was active in the absence of AMP. However, AMP lowered the KM for glucose-1-P to 80 mM for purified phosphorylase b and to 60 mM for the enzyme in crude extract (Ka = 0.5 mM). Using appropriate substrate, buffer and AMP concentrations, assay conditions have been developed which allow determination of phosphorylase a and 90% of the phosphorylase b activity in liver extracts. Interconversion of the two forms can be demonstrated in vivo (under acute stimulation) and in vitro with little change in total activity. A decrease in total phosphorylase activity has been observed after prolonged starvation and in diabetes.
 ...
PMID:Characteristics of the dephosphorylated form of phosphorylase purified from rat liver and measurement of its activity in crude liver preparations. 0 75

Inositol-requiring mutants of Saacharomyces cerevisiae were tested in cell extracts for the ability to convert glucose-6-phosphate to inositol-phosphate (IP synthetase) and inositol (IP phosphatase). Mutants representing any one of 10 unlinked loci conferring the inositol requirement were unable to synthesize either compound in an assay with glucose-6-phosphate as the substrate. These results indicate that the mutants lack IP synthetase activity and that at least 10 genes control the conversion of glucose-6-phosphate to inositol-phosphate. In addition, a mutation known to be unlinked with the ino1 locus interacts with a leaky ino1 allele and may play a role in the regulation of IP synthetase. This mutation causes a 47% reduction in wild-type IP synthetase activity and, when combined in a haploid strain with the leaky ino1 allele, it reduced IP synthetase activity to a level below that which is growth supporting. Wild-type and IP synthetase-deficient strains were tested for reduced nicotinamide adenine dinucleotide (NADH) accumulation, since NAD+ is required in the conversion of glucose-6-phosphate to inositol. No detectable accumulation of NADH was observed in the wild-type strain, presumably because the NADH generated is rapidly oxidized during subsequent partial reactions of IP synthetase. Mutants representing three different loci accumulate NADH and may, therefore, lack the NADH-mediated reductase activity of IP synthetase. Other mutants tested fail to accumulate NADH and may, therefore, lack the NAD+-mediated oxidase activity of IP synthetase. Phospholipid synthesis was studied by 32P pulse labeling in one mutant under conditions of inositol supplementation and starvation. Starved cells incorporate 32P into phospholipids normally for 2 h, followed by a period in which the rate of phosphatidylinositol synthesis decreases and the rate of phosphatidylcholine synthesis increases. After 5 to 6 h starvation, all cellular phospholipid synthesis ceases.
 ...
PMID:Control of inositol biosynthesis in Saccharomyces cerevisiae; inositol-phosphate synthetase mutants. 17 96

The glycogen pellet of dog liver extracts contains a phosphorylase phosphatase which has characteristics different from those of the phosphatases extracted from the cytosol. The phosphatase associated with glycogen is characterized by a M, of 51,000, a half maximal inhibition at 0.3 mM ATP (Hill coefficient : 2) and a Ki for Mg2+ of 1 mM. Treatment with urea or mercaptoethanol of the phosphatase associated with glycogen does not influence the activity, the Mr or the half maximal inhibition by ATP, but a decrease of the Hill coefficient for ATP is observed. A similar treatment of the phosphatases extracted from the high speed supernatant results in a decrease of the Mr of the spontaneously active form from 215,000 to 43,000, without an effect on the Ki for ATP (7 micronM), but accompanied by an increase in activity. The ATP-Mg dependent form of the phosphatase from the high speed supernatant (Mr : 138,000 ; Ka for ATP in the presence of 0.1 mM Mg2+ : 0.3 micronM), is denatured by urea or mercaptoethanol. The phosphatase associated with particulate glycogen cannot be found in the supernatant, nor the phosphorylase phosphatases present in the supernatant in the glycogen pellet. When all the glycogen is mobilized (starvation, glucagon) the phosphatase specifically associated with glycogen cannot be found as such in the cytosol. No activation of synthase beta can be detected neither with the phosphatases extracted from the cytosol nor with the enzyme released from the glycogen pellet.
 ...
PMID:Multiple molecular forms of phosphorylase phosphatase associated with particulate glycogen and extracted from the cytosol of dog liver. 19 25

The regulation of three Salmonella typhimurium phosphatases in reponse to different nutritional limitations has been studied. Two enzymes, an acid hexose phosphatase (EC 3.1.3.2) and a cyclic phosphodiesterase (EC 3.1.4.d), appear to be regulated by the cyclic adenosine 3' ,5'-monophosphate (AMP) catabolite repression system. Levels of these enzymes increased in cells grown on poor carbon sources but not in cells grown on poor nitrogen or phosphorus sources. Mutants lacking adenyl cyclase did not produce elevated levels of these enzymes in response to carbon limitation unless cyclic AMP was supplied. Mutants lacking the cyclic AMP receptor protein did not produce elevated levels of these enzymes in response to carbon limitation regardless of the presence of cyclic AMP. Since no specific induction of either enzyme could be demonstrated, these enzymes appear to be controlled solely by the cyclic AMP system. Nonspecific acid phsphatase activity (EC 3.1.3.2) increased in response to carbon, nitrogen, phosphorus, or sulfur limitation. The extent of the increase depended on growth rate, with slower growth rates favoring greater increases, and on the type of limitation. Limitation for either carbon or phosphorus resulted in maximum increases, whereas severe limitation of Mg2+ caused only a slight increase. The increase in nonspecific acid phosphatase during carbon limitation was apparently not mediated by the catabolite repression system since mutants lacking adenyl cyclase or the cyclic AMP receptor protein still produced elevated levels of this enzyme during carbon starvation. Nor did the increase during phosphorus limitation appear to be mediated by the alkaline phosphatase regulatory system. A strain of Salmonella bearing a chromosomal mutation, which caused constitutive production of alkaline phosphatase (introduced by an episome from Escherichia coli), did not have constitutive levels of nonspecific acid phosphatase.
 ...
PMID:Regulation of two phosphatases and a cyclic phosphodiesterase of Salmonella typhimurium. 19 13

1. The ;initial activity' of the pyruvate dehydrogenase enzyme complex in whole tissue or mitochondrial extracts of lactating rat mammary glands was greatly decreased by 24 or 48h starvation of the rats. Injection of insulin and glucose into starved rats 60min before removal of the glands abolished this difference in ;initial activities'. 2. The ;total activity' of the enzyme complex in such extracts was revealed by incubation in the presence of free Mg(2+) and Ca(2+) ions (more than 10 and 0.1mm respectively) and a crude preparation of pig heart pyruvate dehydrogenase phosphatase. Starvation did not alter this ;total activity'. It is assumed that the decline in ;initial activity' of the enzyme complex derived from the glands of starved animals was due to increased phosphorylation of its alpha-subunit by intrinsic pyruvate dehydrogenase kinase. 3. Starvation led to an increase in intrinsic pyruvate dehydrogenase kinase activity in both whole tissue and mitochondrial extracts. Injection of insulin into starved animals 30min before removal of the lactating mammary glands abolished the increase in pyruvate dehydrogenase kinase activity in whole-tissue extracts. 4. Pyruvate (1mm) prevented ATP-induced inactivation of the enzyme complex in mitochondrial extracts from glands of fed animals. In similar extracts from starved animals pyruvate was ineffective. 5. Starvation led to a decline in activity of pyruvate dehydrogenase phosphatase in mitochondrial extracts, but not in whole-tissue extracts. 6. These changes in activity of the intrinsic kinase and phosphatase of the pyruvate dehydrogenase complex of lactating rat mammary gland are not explicable by current theories of regulation of the complex.
 ...
PMID:The mode of regulation of pyruvate dehydrogenase of lactating rat mammary gland. Effects of starvation and insulin. 21 55

The conversion of glucose into glucose 6-phosphate in an extract of isolated rat hepatocytes incubated in the presence of MgATP was studied spectrophotometrically at 340nm and also by a radiochemical procedure based on the release of (3)H from [2-(3)H]glucose. Both methods gave similar results. The glucose-saturation curve was sigmoidal and the shape of this curve was not influenced by the ionic composition of the incubation medium. The activity at 0.5mm-glucose was only 1-2% of V(max.), indicating a virtual absence of low-K(m) hexokinase in the preparation. The radiochemical method was also used for the determination of glucose phosphorylation by intact hepatocytes. The glucose-saturation curve was also markedly sigmoidal, but the s(0.5) (substrate concentration at half-maximal velocity) and the Hill coefficient were larger than in extracts of hepatocytes. These two parameters became smaller when cells were incubated in a medium in which Na(+) ions were replaced by K(+) ions. The increased rate of phosphorylation at low glucose concentration in a K(+) medium was accompanied by an increased rate of metabolite recycling between glucose and glucose 6-phosphate and also by an increased uptake of glucose. In both media phosphorylation of glucose was inhibited co-operatively by N-acetylglucosamine. Calculations indicate that this inhibition would reach 100% at saturation of the inhibitor, although at lower concentrations of N-acetylglucosamine it was smaller than expected from the known K(i) of N-acetylglucosamine for glucokinase. The rate of phosphorylation of glucose was proportional to the amount of glucokinase in hepatocytes from newborn rats and in conditions such as starvation and diabetes in which the total amount of glucokinase in the liver is decreased. In the same conditions, glucose 6-phosphatase activity was either normal or increased. It is concluded that the phosphorylation of glucose in isolated hepatocytes follows sigmoidal kinetics, which can be explained by the activity of glucokinase alone with no participation of low-K(m) hexokinase or of glucose 6-phosphatase.
 ...
PMID:Phosphorylation of glucose in isolated rat hepatocytes. Sigmoidal kinetics explained by the activity of glucokinase alone. 21 56

In animal tissues the pyruvate dehydrogenase complex is regulated by product inhibition and by a phosphorylation-dephosphorylation cycle catalysed by a kinase and a phosphatase. Physiologic and molecular aspects of this regulation are reviewed, and the results of recent studies are described. Insulin deficiency in the rat (diabetes or starvation) is shown to inhibit the conversion of inactive (phospho-) complex into active (dephospho-) complex by the phosphatase by an effect on the substrate for the phosphatase (phosphorylated complex). This change is stable and persists during isolation, incubation, and extraction of mitochondria or purification of phosphorylated complex. The subunit ratios in the purified pig heart pyruvate dehydrogenase complex and the stoichiometry of phosphorylations have been determined by radioamidination and incorporation of 32P. The ratios of decarboxylase tetramer (alpha 2, beta 2) : dihydrolipoyl acetyltransferase monomer : dihydrolipoly dehydrogenase monomer were 1:1:0.5. Inactivation of the complex was accomplished by incorporation of a single phosphate into one alpha subunit of the decarboxylase tetramer. Two further phosphates are then incorporated and these additional phosphorylations inhibit reactivation of the complex by the phosphate. It is suggested that multisite phosphorylations may inhibit reactivation of the complex by the phosphatase in diabetes and in starvation.
 ...
PMID:Regulation of pyruvate dehydrogenase by insulin action. 23 84

In animals the pyruvate dehydrogenase reaction is mainly responsible for the irreversible loss of glucose carbon by oxidation. Regulation of this reaction is shown to be a major determinant of glucose conservation in starvation and diabetes. Estimates of conservation in man in starvation and diabetes are reviewed. The pyruvate dehydrogenase complex is inhibited by products of its reactions; it is also regulated by a phosphorylation-dephosphorylation cycle catalysed by a kinase intrinsic to the complex and by a more loosely associated phosphatase. Inactivation is largely accomplished by phosphorylation of the tetrameric decarboxylase component (alpha2beta2) to alpha2Pbeta2. Complete phosphorylation produces the (alpha2P3)beta2 form. Both forms are completely reactivated by phosphatase action but the initial rate of reactivation of a complex containing alpha2Pbeta2 is approximately three times that of (alpha2P3)beta2. The proportion of active (dephosphorylated) complex is decreased in rat tissues by starvation and diabetes and in perfused rat heart by oxidation of fatty acids and ketone bodies. In adipose tissue in vitro, insulin increases the proportion of active complex and lipolytic hormones may decrease this proportion. It is suggested that rates of oxidation of lipid fuels may be a major determinant of the activity of pyruvate dehydrogenase in tissues in relation to the actions of insulin and lipolytic hormones and the effects of diabetes and starvation. Phosphorylation and inactivation of the complex are enhanced by high mitochondrial ratios of [acetyl-CoA]/[CoA], [ATP]/[ADP], [NADH]/[NAD+] and low concentrations of pyruvate, Mg2+ and Ca2+, and vice versa.
 ...
PMID:Regulation of pyruvate oxidation and the conservation of glucose. 37 69

An asporogenous mutant of Bacillus megaterium KM, blocked at stage I of sporulation, is cultivated in different conditions which usually lead to sporulation (Nitrogen, carbon, phosphate starvation). Aklaline phosphatase appears only in inorganic phosphate starvation like the wild type, but a glucose dehydrogenase activity also appears in phosphate starvation and so, is dissociated from sporulation.
 ...
PMID:[Variations of enzymatic activities in an asporogenic mutant of Bacillus megaterium for various nutritional deficiencies]. 82 32

The effect of human recombinant tumor necrosis factor (TNF)-alpha on enzymes of gluconeogenesis in the rat was investigated by determining the activity of glucose 6-phosphatase, fructose 1,6-diphosphatase (FDP), and phosphoenolpyruvate carboxykinase in the liver and kidney of fed and fasted rats. The activity of transaldolase in the pentose phosphate pathway was also measured. Starvation of rats for 24 hr resulted in a 1.6- to 3.1-fold increase in liver and kidney glucose 6-phosphatase and phosphoenolpyruvate carboxykinase (P less than or equal to 0.05), a decrease in liver and kidney FDP (P less than 0.002), and an increase in liver and kidney transaldolase (P = 0.0001). Injection of 50 and 100 micrograms/kg/day of TNF for 5 days resulted in a significant (P less than or equal to 0.03) decrease in kidney FDP only. Injection of 100 micrograms/kg/day of TNF for 5 days with a 24-hr fast on Day 5 resulted in a significant (P = 0.04) increase in liver transaldolase, and a significant decrease in kidney FDP and phosphoenolpyruvate carboxykinase. Comparison of the enzyme activities of rats injected with 100 micrograms/kg/day of TNF for 5 days with those of their pair-fed control partners revealed additionally a significant decrease in glucose 6-phosphatase in the liver (P less than 0.001). It is concluded that TNF administration in the rat has different effects on the enzymes of gluconeogenesis in the liver and kidney, and these effects differ from those seen in starved or tumor-bearing rats.
 ...
PMID:Effect of tumor necrosis factor on enzymes of gluconeogenesis in the rat. 130 99


1 2 3 4 5 6 7 8 9 10 Next >>