<P> Certain studies suggested a possible link between a high incidence of amyotrophic lateral sclerosis (ALS) among professional American football players and Italian soccer players, and certain sports supplements including BCAAs . In mouse studies, BCAAs were shown to cause cell hyper - excitability resembling that usually observed in ALS patients . The proposed underlying mechanism is that cell hyper - excitability results in increased calcium absorption by the cell and thus brings about cell death, specifically of neuronal cells which have particularly low calcium buffering capabilities . Yet any link between BCAAs and ALS remains to be fully established . While BCAAs can induce a hyperexcitability similar to the one observed in mice with ALS, current work does not show if a BCAA - enriched diet, given over a prolonged period, actually induces ALS - like symptoms . </P> <P> Blood levels of the BCAAs are elevated in obese, insulin resistant humans and in mouse and rat models of diet - induced diabetes, suggesting the possibility that BCAAs contribute to the pathogenesis of obesity and diabetes . BCAA - restricted diets improve glucose tolerance and promote leanness in mice, and promotes insulin sensitivity in obese rats . </P> <P> Five enzymes play a major role in the parallel synthesis pathways for isoleucine, valine, and leucine: threonine dehydrogenase, acetohydroxyacid synthase, ketoacid reductoisomerase, dihydroxyacid dehygrogenase and aminotransferase . Threonine dehydrogenase catalyzes the deamination and dehydration of threonine to 2 - ketobutyrate and ammonia . Isoleucine forms a negative feedback loop with threonine dehydrogenase . Acetohydroxyacid synthase is the first enzyme for the parallel pathway performing condensation reaction in both steps--condensation of pyruvate to acetoacetate in the valine pathway and condensation of pyruvate and 2 - ketobutyrate to form acetohydroxybtylrate in the isoleucine pathway . Next ketoacid reductisomerase reduces the acetohydroxy acids from the previous step to yield dihydroxyacids in both the valine and isoleucine pathways . Dihydroxyacid dehygrogenase converts the dihyroxyacids in the next step . The final step in the parallel pathway is conducted by amino transferase, which yields the final products of valine and isoleucine . A series of four more enzymes--isopropylmalate synthase, isopropylmalate isomerase, isopropylmalate dehydrogenase, and aminotransferase--are necessary for the formation of leucine from 2 - oxolsovalerate . </P> <P> Degradation of branched - chain amino acids involves the branched - chain alpha - keto acid dehydrogenase complex (BCKDH). A deficiency of this complex leads to a buildup of the branched - chain amino acids (leucine, isoleucine, and valine) and their toxic by - products in the blood and urine, giving the condition the name maple syrup urine disease . </P>

Where do branched chain amino acids come from
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