beta galactosidase assay - (Feb/21/2008 )

hai, has anybody done beta galactosidase activity assay/ONPG assay, using the following equation:


1000*(OD420-[1.75*OD550])/time (min)*vol.(ml)*OD600


if yes would you please explain why 1000 is put in the equation? also, why do we multiply 1.75 with OD550? where do we get 1.75 from?



thanks in advance

i haven't run the assay nor have i used that calculation but...

the 1000* would be to adjust the scale of the units

the 1.75* would probably be a correction factor to match the two wavelengths.