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Updated: Jun 18, 2026

Glutamine Flux Imaging Using Genetically Encoded Sensors
Published on: July 31, 2014
Glutaminyl cyclases display significant catalytic proficiency for glutamyl substrates
Franziska Seifert1, Katrin Schulz, Birgit Koch
1Probiodrug AG, Weinbergweg 22, 06120 Halle, Germany.
Abstract:
N-Terminal glutaminyl and glutamyl residues of peptides and proteins tend to form pyroglutamic acid (pGlu) by intramolecular cylization. The rate constants for spontaneous cyclization of glutamine (10(-6) s(-1)) and glutamic acid (10(-9) s(-1)) in aqueous solution differ by approximately 3 orders of magnitude at pH 6.5. Glutaminyl cyclases (QCs) from plants and mammals accelerate pGlu formation. Human QC exhibits a rate enhancement of 2.2 x 10(5) for glutamate cyclization, approximately 2 orders of magnitude lower than that of the corresponding N-terminal glutaminyl reaction. Thus, glutaminyl cyclases are enzymes with only modest specificity for cyclization of their primary glutaminyl substrates and may provide a link between glutamate cyclization and pathophysiology.
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