CD spectroscopists have often looked at changes in CD signal due to changes in solvent composition such as pH and buff er. In addition, the studies of binding are also often of interest including protein-protein interactions as well as DNA and ligand binding. While these studies are often performed manually the use of automated titration systems has become more popular.
Automatic titration unit
The ATS-530 is designed to automatically monitor changes in CD, absorbance and fluorescence as a function of solution pH, chemical denaturant, or exogenous ligands in experiments such as protein denaturation or ligand binding. Dual syringes are employed, each equipped with a valve for automated refilling/flushing during extended runs and for maintaining a constant cell volume. Additionally, the titration measurement program automatically corrects for concentration.
• Automated titration measurement program included
• Optional macro command program available for complex/custom titrations
• Dual syringes (1 mL volume as standard, 1000 steps/syringe)
• Constant cell volume
• Concentration correction
• pH measurement (optional)
Note: A cell holder with stirrer (PTC-510/517 Peltier thermostatted single cell holder) is required for automatic titration measurement.
Application
Secondary structure changes of poly-L-glutamate during sulfuric acid titration
pH titration is an example of a typical experiment carried out with the ATS-530 system. Here we show the conformational changes of poly-L-glutamate from its random coil to α Helical state while lowering the pH with dilute sulfuric acid.
2D-CD Spectra of sodium poly-L-glutamate titrated with diluted sulfuric acid.
Comparison of experimental and calculated spectrum (before titration).
Comparison of experimental and calculated spectrum (after titration).
Change of SSE abundance ratio of sodium poly-L-glutamate.