Glycine Drives IMP Production in Hybrid Bream (Megalobrama Amblycephala ♀ × Culter Alburnus ♂) Via Concerted Action: Activating glycyl-tRNA Synthetase and Fueling the Pentose Phosphate Pathway.

Inosine monophosphate (IMP), a pivotal umami-enhancing nucleotide abundant in fish muscle, significantly influences palatability. This study investigates the dual regulatory mechanism by which glycine (Gly) promotes IMP biosynthesis in primary myoblasts of hybrid bream (Megalobrama amblycephala ♀ × Culter alburnus ♂, BBTB). We demonstrate that Gly activates glycyl-tRNA synthetase (GARS) and fuels the pentose phosphate pathway (PPP) to synergistically enhance IMP de novo synthesis. Molecular characterization revealed a 2256 bp gars cDNA sequence encoding a 751 amino acid protein in BBTB, with molecular docking confirming Gly-GARS binding. Treatment with 800 µM Gly significantly increased intracellular IMP content and upregulated mRNA expression of eight core IMP biosynthesis genes (gars, gart, paics, adsl, atic, ppat, hprt, ampd1). Crucially, siRNA-mediated gars knockdown in myoblasts completely abolished Gly-induced IMP synthesis and the de novo synthesis pathway, demonstrating that functional GARS is essential for this regulation. Furthermore, Gly enhanced pentose phosphate pathway (PPP) flux by facilitating the synthesis of glutathione (GSH), thereby ensuring the provision of IMP precursors. These findings unveil a novel dual-pathway mechanism: Gly orchestrates IMP biosynthesis through concurrent GARS activation and PPP-driven precursor provision, providing a theoretical foundation for designing amino acid-based feed additives to improve umami quality in aquaculture.