ARTICLE FEED & ADDITIVE MAGAZINE January 2023 57 high protein content diet has also some disadvantages as it is expensive and on utilisation produces excess ammonia in the culture environment which is detrimental to fish. Adequate protein content with suitable amino acid profile and high digestibility increases the protein retention in fish and enhances growth. Maximum utilization of lipid is also highly beneficial for fish which leads to protein sparing for growth and less fat get stored in the fish muscle. Low protein and adequate energy could be a nutritional strategy for fish in the presence of protein synthesizing compound. Nutritional modulation is an efficient way to enhance growth and body composition however, the underlying mechanisms are still largely unknown. Certain substances, such as alpha ketoglutarate (AKG), have been shown to improve protein synthesis and fat utilisation when fed to animals. ALPHA KETOGLUTARATE Glutamine (Gln), and its derivatives, is considered as one of the crucial molecules in protein metabolism, amino acids transport across membranes, gene and cellular redox regulation. However, because of the low solubility and poor stability of glutamine, its precursor α-ketoglutarate (AKG) appears to be more preferable for supplementation. AKG is comprising of two carboxyl groups and a ketone body (Figure 1), also called as 2-ketoglutaric acid, 2-oxoglutamate, 2-oxoglutaric acid, oxo glutaric acid and 2-oxopentanedioic acid, is a rate-determining intermediate in the tricarboxylic acid (TCA) and has a crucial role in cellular energy metabolism. AKG is produced and degraded by a number of different metabolic routes throughout cellular metabolism. In the TCA cycle, AKG is decarboxylated to succinyl CoA and CO2 by AKG dehydrogenase, a key control point of the TCA cycle. Otherwise, AKG can be generated from isocitrate by oxidative decarboxylation catalysed by isocitrate dehydrogenase. Also, AKG can be produced anaplerotically from glutamate (Glu) by oxidative deamination using glutamate dehydrogenase, and as a product of pyridoxal phosphate-dependent trans-amination reactions in which glutamate is a common amino donor. AKG can dissolve well in water, does not show toxic properties and its water solutions characterize has high stability. AKG is the precursor of glutamine and glutamate (Figure 2) and is known to have beneficial effects on protein synthesis, prevents protein degradation in muscles and constitutes an important fuel for gastrointestinal tract cells when provided as a supplement. In the cellular metabolism, it is impossible to utilize AKG from the TCA cycle in the synthesis of amino acids, for this to occur, one must provide AKG as a pure dietary supplement. AKG AND IT’S FUNCTIONS IN AQUACULTURE In several livestock industries, including pig, poultry, and turkey culture, alpha ketoglutarate has been used as a significant feed supplement. HowevFigure 1. 2D & 3D structure of Alpha ketoglutarate Figure 2. Relation between AKG, Glutamine and Glutamate (Ref: Minsoo song et al., 2018)
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