Question

What is the role of aspartate and glutamate in the catabolism of amino acids

Answer 1

Ammonia created during protein breakdown is very toxic and must find its way to the liver, where is converted to urea for excretion. In most cases, the amino groups, separated from amino acids during early steps in the catabolism of proteins, are transferred to α-ketoglutarate to form glutamate. For transport function, glutamate, critical to intracellular amino group metabolism, is supplanted by L-glutamine. The free ammonia produced in tissues is combined with glutamate to yield glutamine. After transport in the bloodstream, the glutamine enters the liver and converts to glutamate by the enzyme glutaminase. In the muscles glutamate can transfer its α-amino group to pyruvate, a readily available product of muscle glycolysis, thus nitrogen will be transported to the liver as amino group of alanine. In hepatocytes, alanine aminotransferase transfers the amino group from alanine to α-ketoglutarate, forming pyruvate and glutamate. In the liver mitochondria glutamate dehydrogenase liberates the amino group of glutamate as ammonium ion (NH4+) that will be used in urea cycle reactions. On the other hand, glutamate can undergo transamination with oxaloacetate to form aspartate, another nitrogen donor in urea synthesis. As we can see, glutamate and aspartate supply the urea cycle.