Protein standard curves: linear regression vs. polynomial fit

Jan van der Lee baslee at
Mon Aug 24 18:45:11 EST 1998

Wolfgang Schechinger wrote:

> Hi all,
> I noticed that when doing Bradford-sytle protein concentration
> measurements, a 2nd order fit (y=ax^2+bx+c) repeatedly seems to be
> smoother than a linear fit (y=ax+b) for the standard curve.
> Has anybody an explanation for this?
> Wolfgang
> -----
> usual disclaimers apply * This message is RNAse free - please don't touch!
> -----
> Wolfgang Schechinger
> University of Tuebingen, Germany
> email: wgschech at * wwWait:
> -------


The actual fit you should use is y= ax + bxy

or: y= (ax)/(1-bx)

The reason: this reaction is limited in final concentration (starts at 0 and has a maximum eg 2.0 in

OD ...

l                            ----------
l                      i
l                  i
l              /
l          /      (example curve)
l       /
l    /
l  /
l /
                                                         (protein conc.)
The curve is only lineair in the lower part.

If you want an/or can use it I could send you a Lotus 1-2-3 spreadsheet with fitting possiblities for all
kinds of curves
Mail me back if you want them.

Regards   Jan (holland)

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