One of the many useful capabilities of NMR is the ability to quantitatively analyze ligand binding in a site specific way. NMRViewJ provides a tool to facilitate the analysis of ligand experiments. The tool provides a way to measure the sequence of chemical shift changes across a set of experiments. This can be done automatically, by finding the most likely path through even overlapped regions. In heavily overlapped regions you can also explicitly select the peaks to be used in the titration fit.
NMRViewJ includes a robust non-linear regression algorithm that can fit a variety of equations. Peak position data can be scaled to account for differential shift ranges on the two axes. Each fit is accompanied by a Monte Carlo simulation to estimate the errors in the fitted parameters. NMRViewJ lets you specify any of the fitted parameters to be held (or bound) to a specific value in the fit (here the parameter A, the chemical shift delta at zero ligand concentration, is fixed to 0). By default (though you can choose a different equation) the titration tool fits the 10^Kd, so the fit value returned is the log(Kd). The Kd display will show you the non-log value. pH titration type data can be fit to a modified Henderson-Hasselbalch equation.
Averaging over multiple titration peaks
As you fit each peak you can add the fit values to a table. NMRViewJ will then display the average Kd and titration profiles for the peaks selected in the table. The fitted lines can be displayed as calculated using the individual Kd values, or the group average. This gives a visual assessment of whether the peaks are titrating with the same dissociation constant. All the accumulated titration information can be exported so you can do your fits and plots with other software if you prefer.