Amino acid aspartate transcarbamylase

Reactions 3 and 4 indicate that with aspartic acid, aspartic transcarbamylase, and carbamyl-P or acetyl-P, either carbamyl aspartate or acetyl aspartate can be formed. Carbamyl aspartate is the first intermediate in the formation of pyrimidines, and acetyl aspartate, of unknown function, is the amino acid derivative present in the largest concentration in brain of most species (43). 

Many protein molecules are composed of more than one subunit, where each subunit is a separate polypeptide chain and can form a stable folded structure by itself. The amino acid sequences can either be identical for each subunit (as in tobacco mosaic virus protein), or similar (as in the a and )3 chains of hemoglobin), or completely different (as in aspartate transcarbamylase). The assembly of many identical subunits provides a very efficient way of constructing... 

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