Like glutamate, aspartate is synthesized by a simple one-step transamination reaction catalyzed by aspartate aminotransferase, AST (formerly referred to as serum glutamate-oxalate transaminase, SGOT). Humans express two different AST enzymes, both of which function as homodimeric enzymes. One AST enzyme is a cytosolic enzyme and the other is a mitochondrial enzyme. The cytosolic AST enzyme is synthesized by the GOT1 gene (glutamate-oxalate transaminase 1) that is located on chromosome – and is composed of 9 exons that encode a 413 amino acid protein. The mitochondrial AST enzyme is synthesized from the GOT2 gene that is located on chromosome 16q21 and is composed of 10 exons that generate two alternatively spliced mRNAs that encode two different isoforms: isoform 1 (430 amino acids) and isoform 2 (387 amino acids).
What is happening with the excess of amino acid carbon skeletons, not needed for energy production? Since the skeletons of both, glicogenic and ketogenic amino acids are metabolized to either acetyl CoA or acetoacetyl CoA, they can be shifted off to fatty acid synthesis. Therefore, excessive intake of dietary protein can also contribute to body fat accumulation, although due to its lower caloric intake relative to that of carbohydrates and fats, as well as its relatively low catabolic usage, significantly less so than these other two macronutrients.