km determination

Simon Easterbrook-Smith sbe at
Sat Dec 5 01:41:11 EST 1998

Dear Mike

It is probably most reliable to fit the M-M equation (v = Vm*S/(Km + S) to
the primary data (pairs of (v, S)) by non-linear regression analysis.

The problem with the various linear plots (Lineweaver-Burke et al.) is that
experimental errors can lead to distortion in the values of the parameter
estimates. Eg, in a Lineweaver-Burke plot large values of 1/v and 1/S have
the biggest effect on the parameter estimates but these data points
(corresponding to small values of v and S) are usually the least accurate.



|| Hello
|| I am currently working to determine the km's of our two different
|| enzymes of interest (isoforms), and am by no means a biochemist.  I am
|| wondering which is the best re-arrangement to determine the actual km. 
|| i have tried some initial data using Lineweaver-Burk plots, Hofstee
|| plats, Woolf plots and Scatchard plots.  Only the Scatchard and
|| Lineweaver-Burk plot agreed.
|| Is there a reference re which is the best plot depending on the data?
|| Should they all agree within a reasonable error?
|| Thanks in advance
|| Mike Allen
|| M.Sc. Student 
|| University of Waterloo
|| Ontario, Canada
|| m3allen at

Dr Simon B Easterbrook-Smith    Voice: (+) 612 9351 3905
Department of Biochemistry      FAX: (+) 612 9351 4726
University of Sydney            Email: sbe at
Sydney NSW 2006
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