G-glutamilhistaminska sintaza (EC6.3.2.18, gama-glutaminilhistamin sintetaza, gama-GHA sintetaza) je enzim sa sistematskim imenom L-glutamat:histamin ligaza.[1] Ovaj enzim katalizuje sledeću hemijsku reakciju
ATP + L-glutamat + histamin produkti ATP razlaganja + Nalfa-gama-L-glutamilhistamin
^Stein, C. & Weinreich, D. (1982). „An in vitro characterization of γ-glutamylhistamine synthetase: a novel enzyme catalyzing histamine metabolism in the central nervous system of the marine mollusk, Aplysia californica”. J. Neurochem. 38: 204—214. PMID6125565.