Why does the determination of protease activity usually use tyrosine as a standard when casein as substrate?
Because of being: abundant, readily purifiable, affordable; relatively stable; and offering desirable biochemical reactivity with detectable signal.
Hi Toto, simplest answer to your first question; BSA is cheap and easily available.
As to your second question, I think that using tyrosine as a standard for casein degradation is more historical than practical. There are papers going back to the '50s and '60 that use this protocol.
When there is a time honored protocol in place, any changes are frowned upon. Plus, casein has more tyrosines than tryptophans.
Hi ,
this is bcoz it is consistently re-constituted at very specific concentrations and very cheap n easily availaible .
I agree with all the comments; however, BSA must NOT be used with the Bradford method because the experimental error you make in your protein determination is around 100%. You can read this even in the Bio-Rad leaflet included with their Bradford reagent. For this purpose is much better ovalbumin, gammaglobulins... For me it is really amazing to read papers in which protein is determined (or I should say estimated) using the Bradford procedure with BSA as a standard!
All the answers above are right. The only other reason BSA is used that I could add is that it was a stable, relatively stable protein that had an 'intermediately sized' molecular mass (as some detection methods give slightly different results depending on either the total peptide content or by the number of certain residues).
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