Rigby D J, Radford A
Biochim Biophys Acta. 1982 Dec 20;709(2):154-9. doi: 10.1016/0167-4838(82)90455-1.
The pyr-3 gene of Neurospora crassa codes for the bifunctional enzyme pyrimidine-specific carbamoyl-phosphate synthetase/aspartate carbamoyltransferase (carbon dioxide: ammonia ligase (ADP-forming, carbamate-phosphorylating)/carbamoylphosphate: L-aspartate carbamoyltransferase), EC 6.3.4.16/EC 2.1.3.2). We describe the investigation of substrate- and product-binding sites of the enzyme by affinity chromatography, using the ligands aspartate, glutamate, and adenosine 5'-diphosphate, and investigate the channelling of carbamoyl phosphate, the product of the first function and substrate of the second, through the pathway. For this latter aspect of the investigation, two new enzyme assays were devised and described. The results of the competition studies on carbamoyl phosphate-binding are consistent with the existence of two different binding sites within the enzyme for this metabolic intermediate, one for it as the product of the first step and the other for it as the substrate of the second.
粗糙脉孢菌的pyr-3基因编码双功能酶嘧啶特异性氨甲酰磷酸合成酶/天冬氨酸氨甲酰转移酶（二氧化碳：氨连接酶（ADP形成，氨基甲酰磷酸化）/氨甲酰磷酸：L-天冬氨酸氨甲酰转移酶），酶编号为EC 6.3.4.16/EC 2.1.3.2。我们描述了利用配体天冬氨酸、谷氨酸和腺苷5'-二磷酸，通过亲和色谱法对该酶的底物和产物结合位点进行的研究，并研究了氨基甲酰磷酸（第一步的产物和第二步的底物）通过该途径的通道作用。对于研究的后一个方面，设计并描述了两种新的酶测定方法。关于氨基甲酰磷酸结合的竞争研究结果与该酶内存在两个不同的该代谢中间体结合位点一致，一个是作为第一步产物的结合位点，另一个是作为第二步底物的结合位点。
