After fitting a curve with two phases or components, how to plot the individual components of a best-fit curve.

The example shows data fit to a two-component binding curve, with dotted and dashed lines showing the two components. This page explains how those curves were generated. Download the Prism file.  It shows the versatility of hooking analysis constants. This example assumes you are using  GraphPad Prism 5. It will not work with earlier versions.

The data were fit with nonlinear regression to the built-in model "Two sites -Specific binding" from the section "Binding - Saturation" . Nonlinear regression fit five parameters: Bmaxi, KdHi, BmaxLo, KdLo, and PercentHiAffinity. 

To generate the dotted and dashed curves:

1. Click Analyze and choose to Create a Family of Theoretical curves. 
2. Enter a range of X values to match the graph (0 to 60). 
3. On the Equation tab, choose the equation, "One site - Specific binding".
4. On the Parameter Value tab, choose to simulate a family of two curves.
5. Click on Curve A to define its parameters. 
6. The first parameter is the Bmax. Don't enter a value. Instead, click on the fish hook icon to hook an analysis constant. 

7. On the Hook Constant dialog, choose best-fit value of BmaxHi, and click ok.

8. Click the other fish hook icon to hook Kd.
9. On the hook constant dialog, choose the best fit value of KdHi. 
10. Repeat for data set B, hooking BmaxLo and KdLo. 

By hooking the icons, the link is live. If you enter new data and so get a different best-fit curve, the two component curves will automatically be recomputed.