{"type": "root", "children": [{"type": "p", "children": [{"type": "t", "text": "\nN-acetylglutamate synthase (NAGS) is a mitochondrial enzyme that plays an essential role in ureagenesis by catalyzing the formation of N‐acetylglutamate (NAG) from glutamate and acetyl‐CoA. NAG is the obligatory allosteric activator of carbamylphosphate synthetase I (CPSI), the first and rate‐limiting enzyme of the urea cycle. The mammalian NAGS gene was identified through its similarity to fungal genes and is highly expressed in liver and small intestine. Its pre‐protein contains an N-terminal mitochondrial targeting signal that, after proteolytic removal, produces mature forms with higher catalytic activity. This basic characterization of NAGS, including its complementation of bacterial mutants and its conserved domain architecture, has provided the foundation for understanding its role in ammonia detoxification."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "1"}]}, {"type": "t", "text": "\n\nNAGS is uniquely regulated by L-arginine, which enhances its enzymatic activity by approximately 2-6-fold. Detailed biochemical analyses have shown that arginine binding not only increases its catalytic turnover but also influences the processing of the pre-protein into mature forms with higher intrinsic activity. Studies employing gene transfer in knockout mouse models and investigations of mutations that abolish arginine activation underscore the physiological importance of this regulatory mechanism. These findings highlight that both the post-translational processing and arginine sensitivity of NAGS are critical for normal ureagenesis."}, {"type": "fg", "children": [{"type": "fg_fs", "start_ref": "3", "end_ref": "5"}]}, {"type": "t", "text": "\n\nIn addition to its catalytic and regulatory aspects, the transcriptional control of the NAGS gene is finely tuned by multiple cis-acting elements and transcription factors responsive to hormonal and dietary cues. Conserved promoter and enhancer regions have been identified that bind factors such as Sp1, CREB, HNF-1, and NF-Y, coordinating the tissue-specific expression of the gene. Moreover, improvements in analytical methods for assessing NAGS activity have been pursued to overcome previous limitations in enzymatic assays, furthering our understanding of its clinical relevance in conditions such as hyperammonemia."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "6"}]}, {"type": "t", "text": "\n"}]}, {"type": "rg", "children": [{"type": "r", "ref": 1, "children": [{"type": "t", "text": "Ljubica Caldovic, Hiroki Morizono, Xiaolin Yu, et al. 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