Zollinger W D, Woodward D O
J Bacteriol. 1972 Mar;109(3):1001-13. doi: 10.1128/jb.109.3.1001-1013.1972.
The possibility of an amino acid substitution (cysteine for tryptophan) in a membrane protein of the [mi-1] strain of Neurospora crassa has been investigated in detail by using a double radioactive labeling procedure. Auxotrophic strains of Neurospora having wild-type [+] or [mi-1] cytoplasm have been grown under conditions which result in the specific labeling of protein tryptophan with (3)H and protein cysteine with (35)S. Although the least soluble 1 to 20% of the [mi-1] mitochondrial membrane protein was usually found to have a higher Cys/Trp ratio (ratio of cysteine plus half-cystine to tryptophan) than the corresponding [+] fraction, it has been shown that these differences were due mainly to the presence of differential amounts of a very insoluble, cysteine-rich (Cys-rich) material. The same Cys-rich material was found in variable amounts in both [+] and [mi-1] cultures, but the concentration was usually higher in the [mi-1] cultures. The Cys-rich material is clearly distinct from "structural protein" on the basis of amino acid composition and appears to have no direct relationship to the [mi-1] phenotype. In the absence of the Cys-rich material, no difference between the Cys/Trp ratios of corresponding [+] and [mi-1] membrane proteins could be detected. We conclude, therefore, that the previously postulated amino acid substitution of cysteine for tryptophan in [mi-1] membrane protein is incorrect.
利用双放射性标记程序，对粗糙脉孢菌[mi-1]菌株膜蛋白中氨基酸取代（半胱氨酸取代色氨酸）的可能性进行了详细研究。具有野生型[+]或[mi-1]细胞质的脉孢菌营养缺陷型菌株在特定条件下培养，该条件可使蛋白质中的色氨酸被³H特异性标记，蛋白质中的半胱氨酸被³⁵S特异性标记。尽管通常发现[mi-1]线粒体膜蛋白中最不溶性的1%至20%部分的半胱氨酸/色氨酸比值（半胱氨酸加半胱氨酸与色氨酸的比值）高于相应的[+]部分，但已表明这些差异主要是由于存在不同量的一种非常不溶性、富含半胱氨酸（Cys-rich）的物质。在[+]和[mi-1]培养物中均发现了不同量的相同富含半胱氨酸的物质，但[mi-1]培养物中的浓度通常更高。基于氨基酸组成，富含半胱氨酸的物质明显不同于“结构蛋白”，并且似乎与[mi-1]表型没有直接关系。在没有富含半胱氨酸的物质的情况下，未检测到相应的[+]和[mi-1]膜蛋白的半胱氨酸/色氨酸比值之间存在差异。因此，我们得出结论，先前假设的[mi-1]膜蛋白中半胱氨酸取代色氨酸的氨基酸取代是不正确的。
