An organic acid that plays a central role in cellular energy metabolism as an intermediate of the citric acid cycle. Also known as alpha-ketoglutarate, it sits at the crossroads of carbohydrate and amino acid metabolism: it can accept ammonia to form glutamate, the most abundant excitatory neurotransmitter and a key nitrogen carrier. This reaction links energy production with nitrogen disposal and amino acid synthesis. In food science and sports nutrition, alpha-ketoglutarate appears in some supplements marketed for exercise performance and recovery, though evidence of benefit in healthy people is limited. Its metabolic centrality makes it a frequent reference point in biochemistry and nutrition texts.