Evidence for reverse flux through pyruvate kinase in skeletal muscle

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Abstract

Conversion of lactate to glucose was examined in myotubes, minced muscle tissue, and rats exposed to 2H2O or 13C- enriched substrates. Myotubes or minced skeletal muscle incubated with [U- 13C3]lactate released small amounts of [1,2,3- 13C3]- or [4,5,6-13C3]glucose. This labeling pattern is consistent with direct transfer from lactate to glucose without randomization in the tricarboxylic acid (TCA) cycle. After exposure of incubated muscle to 2H2O, [U-13C 3]lactate, glucose, and glutamine, there was minimal release of synthesized glucose to the medium based on a low level of 2H enrichment in medium glucose but 50- to 100-fold greater 2H enrichment in glucosyl units from glycogen. The 13C enrichment pattern in glycogen from incubated skeletal muscle was consistent only with direct transfer of lactate to glucose without exchange in TCA cycle intermediates. 13C nuclear magnetic resonance (NMR) spectra of glutamate from the same tissue showed flux from lactate through pyruvate dehydrogenase but not flux through pyruvate carboxylase into the TCA cycle. Carbon from an alternative substrate for glucose production that requires metabolism through the TCA cycle, propionate, did not enter glycogen, suggesting that TCA cycle intermediates do not exchange with phosphoenolpyruvate. In vivo, the 13C labeling patterns in hepatic glycogen and plasma glucose after administration of [U-13C3]lactate did not differ significantly. However, skeletal muscle glycogen was substantially enriched in [1,2,3-13C3]- and [4,5,6-13C 3]glucose units that could only occur through skeletal muscle glyconeogenesis rather than glycogenesis. Lactate serves as a substrate for glyconeogenesis in vivo without exchange into symmetric intermediates of the TCA cycle.

Original languageEnglish (US)
JournalAmerican Journal of Physiology - Endocrinology and Metabolism
Volume296
Issue number4
DOIs
StatePublished - Apr 2009

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Pyruvate Kinase
Skeletal Muscle
Citric Acid Cycle
Lactic Acid
Glucose
Glycogen
Skeletal Muscle Fibers
Pyruvate Carboxylase
Muscles
Liver Glycogen
Phosphoenolpyruvate
Propionates
Random Allocation
Glutamine
Pyruvic Acid
Glutamic Acid
Oxidoreductases
Magnetic Resonance Spectroscopy
Carbon

Keywords

  • Glyconeogenesis
  • Nuclear magnetic resonance
  • Phosphoenolpyruvate carboxykinase
  • Pyruvate kinase
  • Skeletal muscle

ASJC Scopus subject areas

  • Physiology
  • Physiology (medical)
  • Endocrinology, Diabetes and Metabolism

Cite this

@article{6114d396f4244114a0dfb2360b542ad3,
title = "Evidence for reverse flux through pyruvate kinase in skeletal muscle",
abstract = "Conversion of lactate to glucose was examined in myotubes, minced muscle tissue, and rats exposed to 2H2O or 13C- enriched substrates. Myotubes or minced skeletal muscle incubated with [U- 13C3]lactate released small amounts of [1,2,3- 13C3]- or [4,5,6-13C3]glucose. This labeling pattern is consistent with direct transfer from lactate to glucose without randomization in the tricarboxylic acid (TCA) cycle. After exposure of incubated muscle to 2H2O, [U-13C 3]lactate, glucose, and glutamine, there was minimal release of synthesized glucose to the medium based on a low level of 2H enrichment in medium glucose but 50- to 100-fold greater 2H enrichment in glucosyl units from glycogen. The 13C enrichment pattern in glycogen from incubated skeletal muscle was consistent only with direct transfer of lactate to glucose without exchange in TCA cycle intermediates. 13C nuclear magnetic resonance (NMR) spectra of glutamate from the same tissue showed flux from lactate through pyruvate dehydrogenase but not flux through pyruvate carboxylase into the TCA cycle. Carbon from an alternative substrate for glucose production that requires metabolism through the TCA cycle, propionate, did not enter glycogen, suggesting that TCA cycle intermediates do not exchange with phosphoenolpyruvate. In vivo, the 13C labeling patterns in hepatic glycogen and plasma glucose after administration of [U-13C3]lactate did not differ significantly. However, skeletal muscle glycogen was substantially enriched in [1,2,3-13C3]- and [4,5,6-13C 3]glucose units that could only occur through skeletal muscle glyconeogenesis rather than glycogenesis. Lactate serves as a substrate for glyconeogenesis in vivo without exchange into symmetric intermediates of the TCA cycle.",
keywords = "Glyconeogenesis, Nuclear magnetic resonance, Phosphoenolpyruvate carboxykinase, Pyruvate kinase, Skeletal muscle",
author = "Jin, {Eunsook S.} and Sherry, {A. Dean} and Malloy, {Craig R.}",
year = "2009",
month = "4",
doi = "10.1152/ajpendo.90935.2008",
language = "English (US)",
volume = "296",
journal = "American Journal of Physiology - Heart and Circulatory Physiology",
issn = "0363-6135",
publisher = "American Physiological Society",
number = "4",

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TY - JOUR

T1 - Evidence for reverse flux through pyruvate kinase in skeletal muscle

AU - Jin, Eunsook S.

AU - Sherry, A. Dean

AU - Malloy, Craig R.

PY - 2009/4

Y1 - 2009/4

N2 - Conversion of lactate to glucose was examined in myotubes, minced muscle tissue, and rats exposed to 2H2O or 13C- enriched substrates. Myotubes or minced skeletal muscle incubated with [U- 13C3]lactate released small amounts of [1,2,3- 13C3]- or [4,5,6-13C3]glucose. This labeling pattern is consistent with direct transfer from lactate to glucose without randomization in the tricarboxylic acid (TCA) cycle. After exposure of incubated muscle to 2H2O, [U-13C 3]lactate, glucose, and glutamine, there was minimal release of synthesized glucose to the medium based on a low level of 2H enrichment in medium glucose but 50- to 100-fold greater 2H enrichment in glucosyl units from glycogen. The 13C enrichment pattern in glycogen from incubated skeletal muscle was consistent only with direct transfer of lactate to glucose without exchange in TCA cycle intermediates. 13C nuclear magnetic resonance (NMR) spectra of glutamate from the same tissue showed flux from lactate through pyruvate dehydrogenase but not flux through pyruvate carboxylase into the TCA cycle. Carbon from an alternative substrate for glucose production that requires metabolism through the TCA cycle, propionate, did not enter glycogen, suggesting that TCA cycle intermediates do not exchange with phosphoenolpyruvate. In vivo, the 13C labeling patterns in hepatic glycogen and plasma glucose after administration of [U-13C3]lactate did not differ significantly. However, skeletal muscle glycogen was substantially enriched in [1,2,3-13C3]- and [4,5,6-13C 3]glucose units that could only occur through skeletal muscle glyconeogenesis rather than glycogenesis. Lactate serves as a substrate for glyconeogenesis in vivo without exchange into symmetric intermediates of the TCA cycle.

AB - Conversion of lactate to glucose was examined in myotubes, minced muscle tissue, and rats exposed to 2H2O or 13C- enriched substrates. Myotubes or minced skeletal muscle incubated with [U- 13C3]lactate released small amounts of [1,2,3- 13C3]- or [4,5,6-13C3]glucose. This labeling pattern is consistent with direct transfer from lactate to glucose without randomization in the tricarboxylic acid (TCA) cycle. After exposure of incubated muscle to 2H2O, [U-13C 3]lactate, glucose, and glutamine, there was minimal release of synthesized glucose to the medium based on a low level of 2H enrichment in medium glucose but 50- to 100-fold greater 2H enrichment in glucosyl units from glycogen. The 13C enrichment pattern in glycogen from incubated skeletal muscle was consistent only with direct transfer of lactate to glucose without exchange in TCA cycle intermediates. 13C nuclear magnetic resonance (NMR) spectra of glutamate from the same tissue showed flux from lactate through pyruvate dehydrogenase but not flux through pyruvate carboxylase into the TCA cycle. Carbon from an alternative substrate for glucose production that requires metabolism through the TCA cycle, propionate, did not enter glycogen, suggesting that TCA cycle intermediates do not exchange with phosphoenolpyruvate. In vivo, the 13C labeling patterns in hepatic glycogen and plasma glucose after administration of [U-13C3]lactate did not differ significantly. However, skeletal muscle glycogen was substantially enriched in [1,2,3-13C3]- and [4,5,6-13C 3]glucose units that could only occur through skeletal muscle glyconeogenesis rather than glycogenesis. Lactate serves as a substrate for glyconeogenesis in vivo without exchange into symmetric intermediates of the TCA cycle.

KW - Glyconeogenesis

KW - Nuclear magnetic resonance

KW - Phosphoenolpyruvate carboxykinase

KW - Pyruvate kinase

KW - Skeletal muscle

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U2 - 10.1152/ajpendo.90935.2008

DO - 10.1152/ajpendo.90935.2008

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C2 - 19190256

AN - SCOPUS:65649095251

VL - 296

JO - American Journal of Physiology - Heart and Circulatory Physiology

JF - American Journal of Physiology - Heart and Circulatory Physiology

SN - 0363-6135

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