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Regulation of glutamate dehydrogenase (GDH) in response to whole body freezing in wood frog liver linked to differential acetylation and ADP-ribosylation.

Authors
  • Green, Stuart R1
  • Storey, Kenneth B2
  • 1 Institute of Biochemistry & Department of Biology, Carleton University, 1125 Colonel By Drive, Ottawa, K1S 5B6 Ontario, Canada. , (Canada)
  • 2 Institute of Biochemistry & Department of Biology, Carleton University, 1125 Colonel By Drive, Ottawa, K1S 5B6 Ontario, Canada. Electronic address: [email protected] , (Canada)
Type
Published Article
Journal
Archives of Biochemistry and Biophysics
Publisher
Elsevier
Publication Date
Dec 15, 2017
Volume
636
Pages
90–99
Identifiers
DOI: 10.1016/j.abb.2017.10.010
PMID: 29056417
Source
Medline
Keywords
License
Unknown

Abstract

Glutamate dehydrogenase (GDH) represents a critical enzyme catalyzing the reaction spanning amino acid catabolism, the Krebs cycle, and urea production in the wood frog. GDH breaks down glutamate and NAD+ to generate α-ketoglutaric acid (α-KG), NADH and ammonium that can be metabolized to form urea. Purification of GDH from control and frozen male wood frog livers was performed using a two-step column chromatography procedure with a cation exchange column and a GTP-agarose affinity column. Analysis of kinetic parameters of the purified GDH showed several notable differences between the control and stress. Under standard assay conditions, the affinity of GDH for its substrates was significantly higher for the freeze-exposed enzyme than for the control (glutamate Km: 41% decrease, NAD+ Km: 40% decrease). The maximal activity for the control enzyme was also noted to be lower than the frozen. This suggests that the frozen form of the GDH was activated relative to the control form. Western blot analysis of common posttranslational modifications indicated that the frozen enzyme had a lower degree of acetylation and ADP-ribosylation than its control counterpart. These results suggest that GDH is regulated in the wood frog liver by means of altering post-translational modifications in response to freezing.

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