硫代谢调控突变对粗糙脉孢菌中半胱氨酸和高半胱氨酸合成酶水平的影响。

Effect of regulatory mutations of sulphur metabolism on the levels of cysteine- and homocysteine-synthesizing enzymes in Neurospora crassa.

Piotrowska M, Kruszewska A, Paszewski A

Acta Biochim Pol. 1980;27(3-4):395-403.

Abstract

Regulation of four enzymes involved in cysteine and homocysteine synthesis, i.e. cysteine synthase (EC 4.2.99.8), homocysteine synthase (EC 4.1.99.10), cystathionine beta-synthase (EC 2.1.22) and gamma-cystathionase (EC 4.4.1.1) was studied in the wild type and sulphur regulatory mutants of Neurospora crassa. 2. Homocysteine synthase and cystathionine beta-synthase were found to be regulatory enzymes but only the former is under control of the cys-3 - scon system regulating several enzymes of sulphur metabolism, including gamma-cystathionase. 3. The results obtained with the mutants strongly suggest that homocysteine synthase plays a physiological role as an enzyme of the alternative pathway of methionine synthesis. Cysteine synthase activity was similar in all strains examined irrespective of growth conditions. 4. The sconc strain with derepressed enzymes of sulphur metabolism showed an increased pool of sulphur amino acids, except for methionine. Particularly characteristic for this pool is a high content of hypotaurine, a product of cysteine catabolism.

摘要

对粗糙脉孢菌野生型和硫调节突变体中参与半胱氨酸和高半胱氨酸合成的四种酶，即半胱氨酸合酶（EC 4.2.99.8）、高半胱氨酸合酶（EC 4.1.99.10）、胱硫醚β-合酶（EC 2.1.22）和γ-胱硫醚酶（EC 4.4.1.1）的调节进行了研究。2. 发现高半胱氨酸合酶和胱硫醚β-合酶是调节酶，但只有前者受cys-3 - scon系统控制，该系统调节包括γ-胱硫醚酶在内的几种硫代谢酶。3. 用突变体获得的结果强烈表明，高半胱氨酸合酶作为蛋氨酸合成替代途径的一种酶发挥生理作用。无论生长条件如何，在所检测的所有菌株中半胱氨酸合酶活性相似。4. 硫代谢酶去阻遏的scon菌株显示除蛋氨酸外硫氨基酸库增加。该库的一个特别特征是次牛磺酸含量高，次牛磺酸是半胱氨酸分解代谢的产物。