Arginine degradation

Under conditions where optimal sources of nitrogen are unavailable, S. cerevisiae is able to utilize arginine as its sole nitrogen source. Arginine catabolism occurs in the cytosol with the hydrolysis of arginine to proline, releasing three nitrogen atoms that can be used by the cell. In the absence of oxygen, the proline ring is unable to be further degraded. The utilization of arginine as a nitrogen source is repressed if better nitrogen compounds such as ammonia, asparagine or glutamine are present. This is known as nitrogen catabolite repression (NCR). The CAR1 gene is subject to the effect of this repression which is mediated by the negative regulator Ure2p. In the presence of arginine and the absence of a preferred nitrogen source, NCR is released by the GATA transcriptional activators Gln3p and Gat1p. Unrelated to NCR, the presence of arginine also induces CAR1 and CAR2 expression by the regulators Arg80p, Arg81p and Mcm1p. The CAR genes are also activated by the globally acting transcription factors Rap1p and Abf1p. Conversely, CAR1 and CAR2 expression is repressed by the Ume6p-Sin2p-Rpd3p complex. Additionally, CAR2 expression is induced by the two positive regulators Dal81p and Dal82p as well as allophanate, a degradation product of urea. Description from [https://pathway.yeastgenome.org YeastPathways].

在氮源充足条件不足的情况下，酿酒酵母（S. cerevisiae）能够将精氨酸作为其唯一的氮源。精氨酸的代谢过程发生在细胞质中，通过精氨酸的水解生成脯氨酸，释放出三个可供细胞利用的氮原子。在无氧条件下，脯氨酸环无法进一步降解。当存在更优的氮化合物，如氨、天冬酰胺或谷氨酰胺时，精氨酸作为氮源的使用会受到抑制，这种现象被称为氮代谢物抑制（NCR）。受NCR影响的CAR1基因受到负性调节因子Ure2p的调控。在存在精氨酸且缺乏首选氮源的情况下，NCR通过GATA转录激活因子Gln3p和Gat1p得到解除。与NCR无关的是，精氨酸的存在还会通过调节因子Arg80p、Arg81p和Mcm1p诱导CAR1和CAR2的表达。CAR基因还受到全局作用的转录因子Rap1p和Abf1p的激活。相反，CAR1和CAR2的表达受到Ume6p-Sin2p-Rpd3p复合物的抑制。此外，CAR2的表达受到两个正向调节因子Dal81p和Dal82p以及脲的降解产物多聚磷酸盐的诱导。信息来源：[https://pathway.yeastgenome.org YeastPathways]。