Circular dichroism and difference spectra of members of the troponin-tropomyosin system in cetyltrimethylammonium bromide.
The detergent cetyltrimethylammonium bromide (CTAB) was used as a perturbant to study protein structure. Low concentrations of CTAB induced difference spectra for Ac-Trp-OEt and Ac-Tyr-OEt. The delta epsilonM values at their difference maxima were found to be 1300 at 292 nm for Ac-Trp-OEt and 400 at 287 for Ac-Tyr-OEt. These values were used to determine the number of tyrosine residues exposed in tropomyosin and troponin C, as well as the tyrosine and tryptophan residues exposed in troponin I and troponin T. In tropomyosin and troponin C all of the tyorosine residues were accessible to detergent. For TN-T, three of four tyrosines were free while the tryptophan residues were only partially exposed. In the case of TN-I both tyrosines were fully exposed but again evidence was obtained for a partially buried tryptophan chromophore. The stability of these proteins to CTAB was studies by measuring the far-uv circular dichroism spectra. Tropomyosin was quite sensitive to detergent and suffered a 60% loss in ellipticity at the concentration of CTAB used. The troponins, on the other hand, were affected to a lesser extent.
D002593:Cetrimonium Compounds; D002942:Circular Dichroism; D008968:Molecular Conformation; D009124:Muscle Proteins; D010649:Phenylalanine; D011485:Protein Binding; D011487:Protein Conformation; D000644:Quaternary Ammonium Compounds; D013056:Spectrophotometry, Ultraviolet; D014335:Tropomyosin; D014336:Troponin; D014364:Tryptophan; D014443:Tyrosine
D002593:Cetrimonium Compounds; D009124:Muscle Proteins; D000644:Quaternary Ammonium Compounds; D014335:Tropomyosin; D014336:Troponin; D014443:Tyrosine; D010649:Phenylalanine; D014364:Tryptophan