Williams L G, Davis R H
J Bacteriol. 1970 Aug;103(2):335-41. doi: 10.1128/jb.103.2.335-341.1970.
Two carbamyl phosphate synthetases, the first an arginine-synthetic enzyme (CPS(arg)) and the second a pyrimidine-synthetic enzyme (CPS(pyr)), are shown to be present in Neurospora. The two enzymes can be separated on the basis of size and are distinguished by several different properties. Both CPS(pyr) and CPS(arg) have substrate requirements of adenosine triphosphate, HCO(3) (-), and l-glutamine, although NH(4) (+) in high concentration will partially replace glutamine. CPS(pyr) activity can be completely inhibited by 5 x 10(-4) to 10 x 10(-4)m uridine triphosphate (UTP). CPS(pyr) is cold-labile and can be protected against cold inactivation by UTP. The synthesis of CPS(pyr) and aspartate transcarbamylase (ATC), the initial enzymatic steps of the pyrimidine pathway, are co-derepressed by pyrimidine starvation. Mutations affecting CPS(pyr) and ATC all map at the same locus, pyr-3. Three classes of mutants with respect to the two activities were found: CPS(+)ATC(-), CPS(-)ATC(+), and CPS(-)ATC(-). The distribution of these mutants on the genetic map, together with other data, indicate that the two activities are carried by a bifunctional protein.
已证明在粗糙脉孢菌中存在两种氨甲酰磷酸合成酶，第一种是精氨酸合成酶（CPS(arg)），第二种是嘧啶合成酶（CPS(pyr)）。这两种酶可以根据大小分离，并且在几个不同特性上存在差异。尽管高浓度的NH(4) (+) 会部分替代谷氨酰胺，但CPS(pyr)和CPS(arg)都需要三磷酸腺苷、HCO(3) (-) 和L - 谷氨酰胺作为底物。5×10(-4) 至10×10(-4)m的尿苷三磷酸（UTP）可完全抑制CPS(pyr)的活性。CPS(pyr)对低温不稳定，UTP可保护其免受冷失活。嘧啶途径的初始酶促步骤CPS(pyr)和天冬氨酸转氨甲酰酶（ATC）的合成受嘧啶饥饿共阻遏。影响CPS(pyr)和ATC的突变都定位在同一基因座pyr - 3上。发现了关于这两种活性的三类突变体：CPS(+)ATC(-)、CPS(-)ATC(+)和CPS(-)ATC(-)。这些突变体在遗传图谱上的分布以及其他数据表明，这两种活性由一种双功能蛋白承担。
