Defect in glucose metabolism in aortic tissue from alloxan diabetic rabbits

1963 ◽  
Vol 205 (6) ◽  
pp. 1253-1259 ◽  
Author(s):  
Saliha Yalcin ◽  
Albert I. Winegrad
Keyword(s):  
Glucose Utilization ◽  
Aortic Tissue ◽  
Hexokinase Activity ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Glucose Phosphorylation ◽  
Tubular Sections ◽  
Diabetic Rabbits ◽  
Rate Limiting

The glucose, raffinose, and inulin spaces in tubular sections of rabbit thoracic aorta were compared. The glucose space exceeded the raffinose and inulin spaces in tissue from normal rabbits. Insulin in vitro did not alter the relative sizes of the glucose and raffinose spaces in tissue from normal animals. In aortic tissue from alloxan diabetic rabbits, the glucose space exceeded the raffinose space, and the ratio of these spaces was unaltered by insulin in vitro. Hexokinase activity was significantly reduced in tissue from diabetic rabbits. Aortic hexokinase activity was inhibited by glucose 6-phosphate, and no activity resembling hepatic glucokinase was detected. Phosphohexose isomerase and phosphohexokinase activities were not significantly different in normal and diabetic tissues. Transport into cells does not appear to be a rate-limiting step in glucose utilization by aortic tissue from normal or diabetic rabbits incubated in vitro. The impaired glucose utilization previously observed in tissue from diabetic rabbits appears to be related to decreased glucose phosphorylation which may be localized at the hexokinase reaction.

PROGESTERONE AND INSULIN-RESISTANCE: STUDIES OF PROGESTERONE ACTION ON GLUCOSE TRANSPORT, LIPOGENESIS AND LIPOLYSIS IN ISOLATED FAT CELLS OF THE FEMALE RAT

1981 ◽  
Vol 88 (3) ◽  
pp. 455-462 ◽  
Author(s):  
M.-TH. SUTTER-DUB ◽  
B. DAZEY ◽  
E. HAMDAN ◽  
M.-TH. VERGNAUD
Keyword(s):  
Glucose Metabolism ◽  
Pentose Phosphate ◽  
Fat Cells ◽  
Female Rat ◽  
Fat Cell ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Glucose Phosphorylation ◽  
Rate Limiting

The effects of progesterone on isolated rat adipocytes were studied in vitro during various steps of glucose metabolism, transport, lipogenesis and lipolysis. Progesterone decreased the phosphorylation of glucose into glucose-6-phosphate as assessed by measuring the uptake of 2-deoxyglucose but it had no effect on transmembrane transport of glucose as determined by measuring the entry of 3-0-methylglucose into the cell. As glucose phosphorylation is a rate-limiting step of the pentose-phosphate pathway, these data could explain the inhibition of lipogenesis and the enhancement of lipolysis observed when progesterone is present in incubation medium. Progesterone might thus modulate a regulatory step of glucose metabolism and antagonize insulin action in the fat cell.

scholarly journals Determining the Rate-Limiting Step for Light-Responsive Redox Regulation in Chloroplasts

Antioxidants ◽  
2018 ◽  
Vol 7 (11) ◽  
pp. 153 ◽  
Author(s):  
Keisuke Yoshida ◽  
Toru Hisabori
Keyword(s):  
Redox Regulation ◽  
Reducing Power ◽  
Rubisco Activase ◽  
Power Transfer ◽  
Target Proteins ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting

Thiol-based redox regulation ensures light-responsive control of chloroplast functions. Light-derived signal is transferred in the form of reducing power from the photosynthetic electron transport chain to several redox-sensitive target proteins. Two types of protein, ferredoxin-thioredoxin reductase (FTR) and thioredoxin (Trx), are well recognized as the mediators of reducing power. However, it remains unclear which step in a series of redox-relay reactions is the critical bottleneck for determining the rate of target protein reduction. To address this, the redox behaviors of FTR, Trx, and target proteins were extensively characterized in vitro and in vivo. The FTR/Trx redox cascade was reconstituted in vitro using recombinant proteins from Arabidopsis. On the basis of this assay, we found that the FTR catalytic subunit and f-type Trx are rapidly reduced after the drive of reducing power transfer, irrespective of the presence or absence of their downstream target proteins. By contrast, three target proteins, fructose 1,6-bisphosphatase (FBPase), sedoheptulose 1,7-bisphosphatase (SBPase), and Rubisco activase (RCA) showed different reduction patterns; in particular, SBPase was reduced at a low rate. The in vivo study using Arabidopsis plants showed that the Trx family is commonly and rapidly reduced upon high light irradiation, whereas FBPase, SBPase, and RCA are differentially and slowly reduced. Both of these biochemical and physiological findings suggest that reducing power transfer from Trx to its target proteins is a rate-limiting step for chloroplast redox regulation, conferring distinct light-responsive redox behaviors on each of the targets.

scholarly journals The rate-limiting step of protein synthesis in vivo and in vitro and the distribution of growing peptides between the puromycinlabile and puromycin-non-labile sites on polyribosomes

1971 ◽  
Vol 122 (3) ◽  
pp. 267-276 ◽  
Author(s):  
D. C. N. Earl ◽  
Susan T. Hindley
Keyword(s):  
Amino Acids ◽  
Protein Synthesis ◽  
Donor Site ◽  
Peptide Bond ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Donor And Acceptor ◽  
Rate Limiting

1. At 3 min after an intravenous injection of radioactive amino acids into the rat, the bulk of radioactivity associated with liver polyribosomes can be interpreted as growing peptides. 2. In an attempt to identify the rate-limiting step of protein synthesis in vivo and in vitro, use was made of the action of puromycin at 0°C, in releasing growing peptides only from the donor site, to study the distribution of growing peptides between the donor and acceptor sites. 3. Evidence is presented that all growing peptides in a population of liver polyribosomes labelled in vivo are similarly distributed between the donor and acceptor sites, and that the proportion released by puromycin is not an artifact of methodology. 4. The proportion released by puromycin is about 50% for both liver and muscle polyribosomes labelled in vivo, suggesting that neither the availability nor binding of aminoacyl-tRNA nor peptide bond synthesis nor translocation can limit the rate of protein synthesis in vivo. Attempts to alter this by starvation, hypophysectomy, growth hormone, alloxan, insulin and partial hepatectomy were unsuccessful. 5. Growing peptides on liver polyribosomes labelled in a cell-free system in vitro or by incubating hemidiaphragms in vitro were largely in the donor site, suggesting that either the availability or binding of aminoacyl-tRNA, or peptide bond synthesis, must be rate limiting in vitro and that the rate-limiting step differs from that in vivo. 6. Neither in vivo nor in the hemidiaphragm system in vitro was a correlation found between the proportion of growing peptides in the donor site and changes in the rate of incorporation of radioactivity into protein. This could indicate that the intracellular concentration of amino acids or aminoacyl-tRNA limits the rate of protein synthesis and that the increased incorporation results from a rise to a higher but still suboptimum concentration.

scholarly journals Escherichia coli Peptidase A, B, or N Can Process Translation Inhibitor Microcin C

2008 ◽  
Vol 190 (7) ◽  
pp. 2607-2610 ◽  
Author(s):  
Teymur Kazakov ◽  
Gaston H. Vondenhoff ◽  
Kirill A. Datsenko ◽  
Maria Novikova ◽  
Anastasia Metlitskaya ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Cell Growth ◽  
Trna Synthetase ◽  
Methionine Residue ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Translation Inhibitor ◽  
Rate Limiting ◽  
Broad Specificity

ABSTRACT The heptapeptide-nucleotide microcin C (McC) targets aspartyl-tRNA synthetase. Upon its entry into a susceptible cell, McC is processed to release a nonhydrolyzable aspartyl-adenylate that inhibits aspartyl-tRNA synthetase, leading to the cessation of translation and cell growth. Here, we surveyed Escherichia coli cells with singly, doubly, and triply disrupted broad-specificity peptidase genes to show that any of three nonspecific oligopeptidases (PepA, PepB, or PepN) can effectively process McC. We also show that the rate-limiting step of McC processing in vitro is deformylation of the first methionine residue of McC.

scholarly journals Coassembly of SecYEG and SecA Fully Restores the Properties of the Native Translocon

2018 ◽  
Vol 201 (1) ◽  
Author(s):  
Priya Bariya ◽  
Linda L. Randall
Keyword(s):  
Lipid Bilayers ◽  
Rate Constant ◽  
Apparent Rate Constant ◽  
Membrane Vesicles ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Secretory System ◽  
Rate Limiting

ABSTRACTIn all cells, a highly conserved channel transports proteins across membranes. InEscherichia coli, that channel is SecYEG. Many investigations of this protein complex have used purified SecYEG reconstituted into proteoliposomes. How faithfully do activities of reconstituted systems reflect the properties of SecYEG in the native membrane environment? We investigated by comparing threein vitrosystems: the native membrane environment of inner membrane vesicles and two methods of reconstitution. One method was the widely used reconstitution of SecYEG alone into lipid bilayers. The other was our method of coassembly of SecYEG with SecA, the ATPase of the translocase. For nine different precursor species we assessed parameters that characterize translocation: maximal amplitude of competent precursor translocated, coupling of energy to transfer, and apparent rate constant. In addition, we investigated translocation in the presence and absence of chaperone SecB. For all nine precursors, SecYEG coassembled with SecA was as active as SecYEG in native membrane for each of the parameters studied. Effects of SecB on transport of precursors faithfully mimicked observations madein vivo. From investigation of the nine different precursors, we conclude that the apparent rate constant, which reflects the step that limits the rate of translocation, is dependent on interactions with the translocon of portions of the precursors other than the leader. In addition, in some cases the rate-limiting step is altered by the presence of SecB. Candidates for the rate-limiting step that are consistent with our data are discussed.IMPORTANCEThis work presents a comprehensive quantification of the parameters of transport by the Sec general secretory system in the threein vitrosystems. The standard reconstitution used by most investigators can be enhanced to yield six times as many active translocons simply by adding SecA to SecYEG during reconstitution. This robust system faithfully reflects the properties of translocation in native membrane vesicles. We have expanded the number of precursors studied to nine. This has allowed us to conclude that the rate constant for translocation varies with precursor species.

Enhancement of hepatic glycogen by gluconeogenic precursors: substrate flux or metabolic control?

1990 ◽  
Vol 258 (6) ◽  
pp. E899-E906 ◽  
Author(s):  
J. H. Youn ◽  
R. N. Bergman
Keyword(s):  
Glycogen Metabolism ◽  
Hepatic Glycogen ◽  
Glycogen Accumulation ◽  
Major Mechanism ◽  
Rate Limiting Step ◽  
Key Enzyme ◽  
Glucose Phosphorylation ◽  
Rate Limiting ◽  
Gluconeogenic Substrates

After a meal or glucose load, most carbons of hepatic glycogen are derived from gluconeogenesis. In vitro, hepatic glycogen accumulation is sluggish with glucose alone but markedly enhanced in the presence of gluconeogenic substrates. These findings conflict with the classical view that glucose is the major precursor of hepatic glycogen and have been termed the "glucose paradox." In this review, we attempt to elucidate the central mechanism underlying the glucose paradox by critically examining the in vitro data of hepatic glycogen accumulation. Our analysis is inconsistent with the current hypothesis that glucose phosphorylation is rate limiting for hepatic glycogen accumulation from glucose and that gluconeogenesis enhances glycogen accumulation primarily by increasing substrate flux to the hepatic glucose 6-phosphate pool. Instead, our analysis leads us to the conclusion that the rate-limiting step is the net incorporation of glucose 6-phosphate into glycogen, which is synergistically facilitated with glucose and gluconeogenic substrates. Thus gluconeogenic substrates are involved in the regulation of key enzyme(s) of glycogen metabolism. In addition, in the livers from fasted rats there is substantial cycling through glycogen, and that suppression of glycogen degradation may be a major mechanism in the enhancement of glycogen accumulation by gluconeogenic substrates. Thus we propose a specific hypothesis of the role of gluconeogenic substrates in glycogen metabolism (i.e., inhibition of phosphorylase), which can be tested by future studies.

scholarly journals DETERMINATION OF l-HISTIDINE IN NANOGRAM AMOUNTS AND THE QUESTION OF ITS OCCURRENCE IN MAST CELLS

1972 ◽  
Vol 20 (11) ◽  
pp. 917-922 ◽  
Author(s):  
DAVID I. WILKINSON ◽  
DAVID GLICK
Keyword(s):  
Mast Cells ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Peritoneal Mast Cells ◽  
Before And After ◽  
Chromatographic Detection ◽  
Rat Peritoneal Mast Cells ◽  
Rate Limiting

In an attempt to clarify the question of whether histidine is stored in the mast cell for coversion to histamine or whether the rate of conversion is rapid enough to prevent accumulation of histidine so that the rate-limiting step is the histidine uptake, it was found that no histidine was demonstrable in rat peritoneal mast cells by either quantitative analysis or paper chromatographic detection. Microadaptation of Hassall's method, based on conversion of l-histidine by histidase to urocanic acid and measurement of the latter by its absorbance at 277 nm, was made to permit determination of histidine in nanogram amounts in the presence of histamine. This adaptation was found reliable when compared with the o-phthalaldehyde method in estimation of l-histidine in serum and in insulin hydrolysate, and then it was applied to analysis of mast cells before and after l-histidine uptake in vitro. The adaptation should be generally useful in microanalysis of l-histidine in histologically and cytologically defined samples.

scholarly journals IMMU-43. POLYAMINE METABOLISM REGULATES MYELOID IMMUNE SUPPRESSION IN GLIOBLASTOMA

2019 ◽  
Vol 21 (Supplement_6) ◽  
pp. vi128-vi128
Author(s):  
Jason Miska ◽  
Catalina Lee Chang ◽  
Aida Rashidi ◽  
Yu Han ◽  
Aurora Lopez-Rosas ◽  
...  
Keyword(s):  
Immune Suppression ◽  
De Novo ◽  
Specific Inhibitor ◽  
Suppressor Cells ◽  
Polyamine Metabolism ◽  
Arginase 1 ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting

Abstract Tumor-associated myeloid cells, which consist of tumor associated macrophages and myeloid-derived suppressor cells (MDSCs), make up a majority of cellular infiltrates in glioma. Glioma infiltrating MDSCs highly express arginase-1 (Arg-1), a catabolic enzyme thought to deplete arginine from the tumor microenvironment. Despite being a well-known marker of immunosuppressive cells, the metabolic reasons for this choice are not clear. Examination of MDSC phenotype in murine glioma models using: RNA-seq, bulk metabolomics, and Carbon-13 arginine flux revealed that two separate pathways of arginine catabolism converge on the generation of ornithine. Ornithine is the prerequisite substrate for the de-novo generation of polyamines, a group of nitrogen-rich metabolites with foundational importance to all mammalian, bacterial, and plant biology. Importantly, we found that the rate-limiting step of polyamine generation, ornithine decarboxylase 1 (ODC1), is dramatically upregulated by glioma infiltrating MDSCs, suggesting de-novo polyamine generation is important for MDSC function. Treatment with a specific inhibitor of de-novo polyamine synthesis, difluoromethylornithine (DMFO), inhibited the immunosuppressive function of in-vitro generated glioma associated MDSCs. However, DFMO only exerted effects before differentiation, as DFMO treatment post-generation did not change their suppressive functions. This suggests that the generation of the polyamine pool is critical to immune suppression by MDSCs. Interestingly the expression of the rate limiting step of polyamine degradation (SAT1) is inversely correlated with (ODC1) during MDSC differentiation, suggesting that utilization of this polyamine pool may be required for the suppressive functions of these cells. Inhibition of SAT1 after MDSC generation blunted MDSC mediated T-cell suppression. The results of this study show that the role of arginine metabolism in tumor infiltrating MDSCs is to generate pools of polyamines which maintain MDSC function in glioma. Therapeutic targeting of this pathway may be a novel and powerful tool to combat immunosuppression in glioma.

scholarly journals Coupled Glucose Transport and Metabolism in Cultured Neuronal Cells: Determination of the Rate-Limiting Step

1995 ◽  
Vol 15 (5) ◽  
pp. 814-826 ◽  
Author(s):  
Richard R. Whitesell ◽  
Michael Ward ◽  
Anthony L. McCall ◽  
Daryl K. Granner ◽  
James M. May
Keyword(s):  
Glucose Transport ◽  
Glucose Utilization ◽  
Neuroblastoma Cell ◽  
Neuronal Cells ◽  
Neuronal Cell ◽  
Cell Types ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting ◽  
Intracellular Glucose

In brain and nerves the phosphorylation of glucose, rather than its transport, is generally considered the major rate-limiting step in metabolism. Since little is known regarding the kinetic coupling between these processes in neuronal tissues, we investigated the transport and phosphorylation of [2-3H]glucose in two neuronal cell models: a stable neuroblastoma cell line (NCB20), and a primary culture of isolated rat dorsal root ganglia cells. When transport and phosphorylation were measured in series, phosphorylation was the limiting step, because intracellular glucose concentrations were the same as those outside of cells, and because the apparent Km for glucose utilization was lower than expected for the transport step. However, the apparent Km was still severalfold higher than the Km of hexokinase I. When [2-3H]glucose efflux and phosphorylation were measured from the same intracellular glucose pool in a parallel assay, rates of glucose efflux were three- to-fivefold greater than rates of phosphorylation. With the parallel assay, we observed that activation of glucose utilization by the sodium channel blocker veratridine caused a selective increase in glucose phosphorylation and was without effect on glucose transport. In contrast to results with glucose, both cell types accumulated 2-deoxy-d-[14C]glucose to concentrations severalfold greater than extracellular concentrations. We conclude from these studies that glucose utilization in neuronal cells is phosphorylation-limited, and that the coupling between transport and phosphorylation depends on the type of hexose used.

FURTHER OBSERVATIONS ON THE FUNCTIONAL ZONATION OF THE ADRENAL CORTEX

1964 ◽  
Vol 42 (12) ◽  
pp. 1777-1786 ◽  
Author(s):  
J. Stachenko ◽  
C. J. P. Giroud
Keyword(s):  
Adrenal Cortex ◽  
Zona Glomerulosa ◽  
Hydroxylase Activity ◽  
In Vitro System ◽  
Steroid Molecule ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Main Action ◽  
Rate Limiting

In the isolated zona glomerulosa of beef adrenal cortex, progesterone, 11β-hydroxyprogesterone, 11-desoxycorticosterone, and corticosterone are precursors of aldosterone. 18-Hydroxylation is probably a rate-limiting step in the biosynthesis of aldosterone. At low concentration Metopirone selectively inhibits 18-hydroxylase activity. The sequence of hydroxylation of the steroid molecule proceeds effectively in the order 11, 17, 21. The main action of ACTH is to increase cortisol production by the fasciculate–reticularis. In the present in vitro system, the production of aldosterone by the glomerulosa is not affected by either ACTH or angiotensin.

Sign in / Sign up

Export Citation Format

Share Document