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Glutamate formation via the leucine-to-glutamate pathway of rat pancreas.

American journal of physiology. Gastrointestinal and liver physiology (2014-04-05)
David Schachter, Jean Buteau
ABSTRACT

The leucine-to-glutamate (Leu→Glu) pathway, which metabolizes the carbon atoms of l-leucine to form l-glutamate, was studied by incubation of rat tissue segments with l-[U-(14)C]leucine and estimation of the [(14)C]glutamate formed. Metabolism of the leucine carbon chain occurs in most rat tissues, but maximal activity of the Leu→Glu pathway for glutamate formation is limited to the thoracic aorta and pancreas. In rat aorta, the Leu→Glu pathway functions to relax the underlying smooth muscle; its functions in the pancreas are unknown. This report characterizes the Leu→Glu pathway of rat pancreas and develops methods to examine its functions. Pancreatic segments effect net formation of glutamate on incubation with l-leucine, l-glutamine, or a mix of 18 other plasma amino acids at their concentrations in normal rat plasma. Glutamate formed from leucine remains mainly in the tissue, whereas that from glutamine enters the medium. The pancreatic Leu→Glu pathway uses the leucine carbons for net glutamate formation; the α-amino group is not used; the stoichiometry is as follows: 1 mol of leucine yields 2 mol of glutamate (2 leucine carbons per glutamate) plus 2 mol of CO2. Comparison of the Leu→Glu pathway in preparations of whole pancreatic segments, isolated acini, and islets of Langerhans localizes it in the acini; relatively high activity is found in cultures of the AR42J cell line and very little in the INS-1 832/13 cell line. Pancreatic tissue glutamate concentration is homeostatically regulated in the range of ∼1-3 μmol/g wet wt. l-Valine and leucine ethyl, benzyl, and tert-butyl esters inhibit the Leu→Glu pathway without decreasing tissue total glutamate.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
L-Valine, from non-animal source, meets EP, JP, USP testing specifications, suitable for cell culture, 98.5-101.0%
Sigma-Aldrich
L-Leucine, from non-animal source, meets EP, JP, USP testing specifications, suitable for cell culture, 98.5-101.0%
Sigma-Aldrich
L-Leucine, reagent grade, ≥98% (HPLC)
Sigma-Aldrich
L-Valine, reagent grade, ≥98% (HPLC)
Sigma-Aldrich
L-Valine, BioUltra, ≥99.5% (NT)
Sigma-Aldrich
L-Leucine, BioUltra, ≥99.5% (NT)
SAFC
L-Valine
Supelco
L-Leucine, certified reference material, TraceCERT®
Supelco
L-Valine, certified reference material, TraceCERT®
Sigma-Aldrich
L-Leucine, 99%, FG
USP
L-Leucine, United States Pharmacopeia (USP) Reference Standard
Supelco
L-Leucine, Pharmaceutical Secondary Standard; Certified Reference Material
Supelco
L-Valine, Pharmaceutical Secondary Standard; Certified Reference Material
Sigma-Aldrich
L-Glutamine
Sigma-Aldrich
L-Glutamine, BioUltra, ≥99.5% (NT)
SAFC
L-Glutamine
Sigma-Aldrich
L-Glutamine, meets USP testing specifications, suitable for cell culture, 99.0-101.0%, from non-animal source
Sigma-Aldrich
L-Glutamine, γ-irradiated, BioXtra, suitable for cell culture
Sigma-Aldrich
L-Glutamine, ReagentPlus®, ≥99% (HPLC)
Supelco
L-Glutamine, Pharmaceutical Secondary Standard; Certified Reference Material
Supelco
L-Glutamine, certified reference material, TraceCERT®