Biorad Protein Concentrations

[LYNDON at BMS-UNIT.ICR.AC.UK]

Can anybody make any reccomendations for a standard protein for the Biorad
protein assay .... Ig G and BSA seem to vary significantly from one another
in terms of absorbtion at a given concentration. Are there any rules such
as use protein x if your sample contain n number of whatever residues??
The Biorad assay seems to be extensively used but very inaccurate! I know I
could determine the molar absorbtion coeff. but I do not have enough protein to
do this.
Any ideas greatly appreciated,

Lyndon.