The program calculates steady state equilibria, simulates dynamic equilibria, and calculates dissociation constants. The analysis is available in numeric and graphic form. 

Examples of biochemical interactions include signal transduction receptors binding their ligand, transcription factors binding to their cognate sequence element in DNA, and regulatory subunits  of enzymes interacting with the catalytic subunit.

More detailed information about Equilibrate

Introduction

Equilibrate is a program for calculating equilibria and dissociation constants for molecules that interact with each other. Examples of biochemical interactions that occur in living organisms or in vitro include signal transduction receptors binding their ligand, transcription factors binding to their cognate sequence element in DNA, regulatory subunits of enzymes interacting with the catalytic subunit, and so on.

The extent to which the molecules bind to each other is dependent on a variety of factors, including concentration of the molecules, ionic strenth (mono- and bivalent cations), temperature and so on. In addition, binding is seldomly irreversible. The extent of binding under a defined set of condtions is described by the dissociation constant, K_D (or by the inverse, the association constant, K_A).

These interactions are of the type:

A + B <==> [A/B]

K_D = [A] [B] / [AB]

Features of Equilibrate

Equilibrate provides three utilities which work with graphic routines that support publication quality figures: 

(1) The Equilibrium Tool calculates steady state equilibria on basis of a minimum of three pieces of data entered by the user. It calculates the remaining, unknown variables. In addition, it plots a graph showing the steady state equilibrium at a range of concentrations. 

(2) The Dynamic Equilibrium Tool allows to perform a simulation of real time kinetics of the interaction between two molecules. The tool allows the user to analyze the concentration of the molecules and the rate with which the concentration changes as a function of time. The tool also features a "Programmed Events" option, which allows the user to perturb the equilibrium by increasing or decreasing the concentration of one or more molecules at any given time. The software plots a graph to facilitate the analysis, in addition the simulation data are available in numeric form. 

(3) The Scatchard Analysis Tool calculates the dissociation constant (K_D) of the interaction using three pieces of experimental data as a minimum. It is known that the ratio of Bound-to-Free of one of the components is a linear function of the concentration of Bound. Using linear regression the data are analyzed statistically, including the calculation of a 95% confidence interval for the calculated K_D The experimental data are plotted in a graph, along with the best fit of the linear regression analysis.

The graph is highly customizable, supporting the following features:
Selection of variables to be plotted on the X and Y axes
Selection of a linear or logarithmic scale
Specifying the range of X and Y to be plotted
Editing X and Y axis titles
Moving and resizing the axis titles
Selection of preferred units
Multiple graphs in one chart
Copying the graph to the Windows clip board
Printing the graph

Using the multiple graph option the user is able to get a more intuitive understanding of the effect of a different dissociation constant (KD) on the equilibrium at a range of concentrations, or to plot the concentration of all the different components in the interaction in one chart. 

The Equilibrate user interface

(1) The Equilibrium Tool calculates steady state equilibria on basis of a minimum of three pieces of data entered by the user in the Equilibrium Tool window (left hand window in Fig. 1). It calculates the remaining three variables. In addition, it plots a graph showing the steady state equilibrium at a range of concentrations (right hand window in Fig. 1). With the multiple graph option the user is able to get an intuitive understanding of the effect of a different dissociation constant (K_D) on the equilibrium at a range of concentrations, or to plot the concentration of all the different components in the interaction in one chart.

Figure 2 (Click on image to enlarge)

(2) The Dynamic Equilibrium Tool allows to perform a simulation of real time kinetics of the interaction between two molecules. This tool allows the user to analyze the concentration of the molecules and the rate with which the concentration changes as a function of time. 

This tool features a "Programmed Events" option, which allows the user to perturb the equilibrium by increasing or decreasing the concentration of one or more molecules at any given time. This shows in the graph as a sudden increase (or decrease) followed by a slower equilibration (right hand window in Fig. 2).

Figure 3 (Click on image to enlarge)

(3) The Scatchard Analysis Tool calculates the dissociation constant (K_D) of the interaction using three pieces of experimental data as a minimum (maximum is 20) entered by the user in the Scatchard Analysis Tool window (left hand window in Fig. 3). 

It is known that the ratio of Bound-to-Free of one of the components is a linear function of the concentration of Bound. Using linear regression the data are analyzed statistically, including the calculation of a 95% confidence interval for the calculated K_D. The experimental data are plotted in a graph, along with the best fit of the linear regression analysis (right hand window in Fig. 3).

Download Equilibrate

Equilibrate is freeware. Check the system requirements and obtain your copy now.

Frequently Asked Questions

Download problems with the Homestead site
Problems with unzipping the downloaded file and / or running setup.exe
Sites Equilibrate (version 1.2) be downloaded from

If I try to download a file from the Homestead site I get the following error message: "Cannot Download this File. This type of file can only be downloaded via a page created at Homestead www.homestead.com)." Why?
Homestead only allows downloads from one of their own pages. So if you tried to download a file stored on a Homestead server from a non-Homestead web page, go to the Homestead - Equilibrate download page and try again.
If you have done that, and you still experience problems, chances are that you are using the Netscape SmartDownload utility. The solution to that problem is either not to use SmartDownload (click the Advanced button while using SmartDownload) or use another website to download Equilibrate software. For hyperlinks see below.

I downloaded the Equilibrate installation file as a zipped archive (eq12.zip / equilibr.zip) but I could not unzip the file and / or run setup.exe that is contained in it. What is the problem?
First, make sure that you use a zip utility that is compatible with WinZip. If you happen to use a program called Stuffit, you need to use a different utility as Stuffit is known to cause problems with unzipping the archive as it adds a '//' in the path of the folder which makes it unrecognizable by Windows.
If you are using WinZip or a 100% compatible utility and still it does not work, make sure the file did not get corrupted during download (see below for other download links).
Thirdly, check also the system requirements of the software.

What sites can Equilibrate (version 1.2) be downloaded from?
Equilibrate 1.2 can be downloaded from the following sites:
Equilibrate.Homestead.com
winsite.com 1
winsite.com 2
FTP sites:
ftp://ftp.kddlabs.co.jp/.3/WinSite/win95/misc/eq12.zip
ftp://ftp.uni-marburg.de/mirror/winsite.com/win95/misc/eq12.zip
ftp://ftp.rediris.es/mirror/winsite/winsite-95/misc/eq12.zip
ftp://ftp.uni-heidelberg.de/pub/cica/win95/misc/eq12.zip
ftp://ftp.the.net/pub/mirrors/ftp.winsite.com/pc/win95/misc/eq12.zip
ftp://ftp.funet.fi/pub/mirrors/ftp.winsite.com/pub/pc/win95/misc/eq12.zip
ftp://ftp.monash.edu.au/pub/win95/misc/eq12.zip
ftp://ftp.sunet.se/pub2/pc/windows/mirror-cica/win95/misc/eq12.zip

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Check out our Fequently Asked Questions page if you have a question. Also if you have a problem with downloading or installing Equilibrate, please check out this page first.

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