Calculation of the molecular weight of proteins from electrophoretic and gel exclusion chromatographic experiments

The molecular weights of proteins or protein subunits are frequently estimated from the electrophoretic mobility in the presence of sodium dodecyl sulphate, or from the elution volume in gel filtration chromatography. Using a series of standards of known size, a calibration curve is prepared which often yields a straight line in a semilogarithmic plot; interpolation from this line then gives the size of the sample. While this method is simple to apply, it does not give any estimate of the accuracy of the determined size. Furthermore there is no objective criterion for deciding if the calibration curve is linear, or a procedure for dealing with non-linear calibration curves. Here I report a method and a computer program which uses appropriate statistical methods to select the best straight or curved calibration line. The size of the unknown is then interpolated and an estimate or the error in this value is calculated.