Using 4-parameter fit for colorimetric assays for protein concentration? - how appropriate is it.. higher concentraion.. no linearity? (Jun/22/2008 )

hi all.. how appropriate is it.. to use the 4-parameter fit for colorimetric assays for protein concentration? ideally a linear range should be selected where OD vs COncnetration does not reach saturation in terms of the reaction right?
the why do certain microbca and bradford kits recommend 4-pl fit?
thankss

---

Alice,
The advantage of linear models is that they can cancel out some error/noise in data if you know the relationship must be linear under the conditions used. This is rarely the case except over relatively small concentration ranges. There is nothing wrong with using a higher order model to fit data that spans a more practical concentration range. This will provide better interpolation over a wider range where there may be some saturation behavior. Be careful to avoid having so many parameters that you see "extra" curvature between standards and also keep in mind that your assay will be most sensitive where the slope of the calibration curve is steepest.

jeff

---