Kinetics of General Enzyme Modifier Mechanism of Botts-Morales

with the model nomenclature of Prof. Baici

Ref.: Antonio Baici, Kinetics of Enzyme-Modifier Interactions, Springer-Verlag, Vienna

Purchase EZ-Fit-Ki $9.99 - New Version

New Improved Version 5.0 (May 15, 2024)

All users of EZ-Fit-Ki are encouraged to download the latest version of EZ-Fit-Ki. Users with an active license can download and activate the software with their current activation code. If anyone encounters an issue with EZ-Fit-Ki, please let us know via out email (

EZ-Fit-Ki performs nonlinear regression curve-fitting of data to the Botts-Morales General Modifier enzyme kinetic inhibition mechanisms selected from in internal library of 10 linear and hyperbolic models as defined in Prof. Baici's book (2) .

EZ-Fit-Ki is priced to make it affordable to professionals and students alike. But don't let the low price mislead you. EZ-Fit-Ki is robust and powerful using some of the most sophisticated regression algorithms, including Quadratic Programming, Conjugate Gradient , and Nelder-Mead Simplex methods. Why pay hundreds and yearly license fees when you can have curve-fitting software for a fraction of the cost. Best of all, there are no time limit restrictions or number of uses.

With just a couple of clicks of the mouse, EZ-Fit-Ki simplifies curve fitting your data to enzyme inhibition models. Select one or more equations from an internal library of 10 models, and EZ-Fit-Ki does the rest by fitting the curve to your data set, displaying the statistical results, model parameters, the best fit curve, and the residuals. Plots displayed include Rate vs [S], Residuals of curve-fit, Kmapp vs [I], and MC50 vs [S].

The EZ-Fit-Ki results of your curve-fit includes the fitted parameters, their standard errors , confidence limits, correlation matrix, gradients, and corrected Akaike value. The plots displayed include Rate vs [S], Residuals of curve-fit, Kmapp vs [I], and MC50 vs [S].

Reaction scheme of General Modifier (Botts-Morales) Mechanism

[E]: enzyme, [ES]: enzyme-substrate complex, [ESI]: enzyme-substrate-inhibitor complex, [S]: substrate, [I]: inhibitor, [P]: product of reaction, Km: substrate dissociation constant, Ki: inhibitor binding dissociation constant, and 'a' and 'b' are dimensionless parameters that define the type of the inhibition mechanism.

The library of enzyme inhibition models is based on the rapid-equilibrium assumption and describes the basic mechanisms for the all common reversible inhibition mechanisms. Please note that the quasi-equilibrium assumption for the mechanism under investigation may not always apply. Therefore, the user is advised to check for tight-binding inhibition before using any model equation in this software. At saturating inhibitor concentrations the enzyme activity is either fully or partially inhibited depending on the value of parameter 'b'. The inhibition response can be either linear (b = 0) or partial (0 < b < 1). If b = 1 then both [ES] and [ESI] are equally catalytically active. In contrast, when b = 0 then only the [ES] complex forms product. The factor 'a' represents the difference in binding affinities between the substrate binding to the [EI] complex and the inhibitor binding to the [ES] complex. When a = 1 the binding is equal, but when a = 0, inhibitor only binds to the free enzyme. Differing values of 'a' and 'b' can be used to obtain the common types of inhibition models. Linear and hyperbolic competitive, uncompetitive, noncompetitive, or mixed type inhibition can generally be distinguished by the values of parameters 'a' and 'b'. When more than one model produces similar best curve-fits, it is advised to follow the principle of parsimony and select the mechanism that is the simplest of the competing mechanisms.


1- Botts J, Morales M (1953) "Analytical description of the effects of modifiers and of enzyme multivalency upon the steady state catalyzed reaction rate", Trans Faraday Soc 49: 696-707.

2- Antonio Baici (2015) ''Kinetics of Enzyme-Modifier Interactions'', © Springer-Verlag Vienna.

Nonlinear regression curve-fitting software at an affordable price.

Download Software at bottom of page...

EZ-Fit-Ki for MS Windows­
EZ-Fit-Ki for MS Windows­

Quality software at a reasonable price.

Purchase using PayPal or Credit Card (VISA or MasterCard)

buy ez-fit-ki­
PayPal uses the latest technology and proprietary procedures to protect the security of its transactions. PayPal automatically encrypts your confidential information in transit from your computer to theirs.

Download the latest version of EZ-Fit-Ki

Download the software zip file to a single folder, Unzip it and then run EZ-Fit-Ki.exe to obtain the registration code to unlock the software on your computer. Then purchase EZ-Fit-Ki using PayPal and email the registration code to us at No Windows installation is required; just drop it into a folder and run. The zip file also contains example data files.

Note: The generated EZ-Fit-Ki.lic file must reside in the same folder as EZ-Fit-Ki.exe. A text editor (e.g., Notepad) must be used to create and save all data files. A Notepad is available in the File/Edit Data File menu to revise and edit data.dat files once the data file is Opened.

Download and unZip the file in a folder (e.g., C:\MyEZ-Fit-Ki\) on a computer you choose to license the software, and then run EZ-Fit-Ki.exe to retrieve the "Registration Code". The lack of formal Windows installation is intentional, as it allows installation without administrative privileges (no dynamic link libraries (DLL) are used) and no network connection. After you've paid for the software using PayPal, email us the Registration Code at and we'll send you the Activation Code to enter and fully activate the software. Once activated, do not delete or modify the lic file contained therein as it is required to execute and run the software. We suggest that you make backup copies of both the EZ-Fit-Ki.exe and EZ-Fit-Ki.lic files for future reference. EZ-Fit-Ki is copy-protected to run on one MS Windows 32 or 64-bit computer.
Note: has been scanned by Windows Defender.

File size: 594.12 KB

Download the EZ-Fit-Ki ZIP file to your computer and unzip the file in a folder on your computer.


Note: If your browser flags the downloaded zip file with a cautionary warning, you have the option of selecting "keep" to continue the download process. The file was scanned with Microsoft Windows Defender and shown not to have any detectable threats. The EZ-Fit-Ki software does not send any information back to us or anyone else, and it does not require a network connection to run. It is a standalone executable file (no DLL files) .

Disclaimer of 'False Positive' virus: EZ-Fit-Ki.exe is an independently distributed program, and as such EZ-Fit-Ki.exe may be flagged as a 'false positive' by your antivirus/antimalware software. Therefore, it is advisable to create an exclusion for the EZ-Fit-Ki.exe software to avoid the appearance of 'false positive' errors during execution.