title: Comparison of cysteine and tryptophan content of insoluble proteins derived from wild-type and mi-1 strains of Neurospora crassa.
abstract: 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.
mesh_terms: D001322:Autoanalysis; D002458:Cell Fractionation; D002499:Centrifugation, Density Gradient; D003470:Culture Media; D003545:Cysteine / Q000032:analysis*; D003576:Electron Transport Complex IV / Q000378:metabolism; D004589:Electrophoresis, Disc; D005827:Genetics, Microbial; D008928:Mitochondria / Q000032:analysis; D009491:Neurospora / Q000032:analysis*; D009492:Neurospora crassa / Q000032:analysis / Q000201:enzymology / Q000254:growth & development; D010641:Phenotype; D011506:Proteins / Q000032:analysis*; D012995:Solubility; D013045:Species Specificity; D013053:Spectrophotometry; D013395:Sucrose; D013460:Sulfur Isotopes; D014316:Tritium; D014364:Tryptophan / Q000032:analysis*; D062367:ortho-Aminobenzoates
chemical_list: D003470:Culture Media; D011506:Proteins; D013460:Sulfur Isotopes; D062367:ortho-Aminobenzoates; D014316:Tritium; D013395:Sucrose; D014364:Tryptophan; D003576:Electron Transport Complex IV; D003545:Cysteine