1) Hi, Do you know that NIBS 98/574 standard is used in SDS-PAGE?
(in this standard COA, it's not mentioned that the above standard is suitable for SDS-PAGE or not?)
2) why my recombinant human growth hormone (my host is E.coli) has the molecular weight lower than expected (about 19 kD & expected MW is about 22 kD).
I'm using from 2ME+Biorad sample buffer and also I heat my samples 5 min at 100 C.
The NIBSC standards are intended for measuring activity. It would not normally be necessary to use it in SDS-PAGE, because there are definitive standard-free methods available to determine the molecular weight, sequence and chemical identity of your molecule. Mass spec would generally useful for those things. If you have access to plenty of standard, there's no reason not to use it in SDS-PAGE.
I would not be too concerned by the small difference between expected and observed Mw that you see. SDS-PAGE is affected by the sequence of some proteins. Does the standard sequence migrate abnormally too? Is your sequence in fact identical to the standard? (Some growth hormone preparations may contain additional residues -- purification tags, residues of protease sites, clutter from cloning, etc). Make sure you understand any sequence differences.
In any case, you should use a more definitive method to confirm your sequence (mass spec).
@John Schloendorn: thanks. my NIBS standard also has the MW look like my sample(about 19 kD).
I think this is just splendid. Your growth hormone looks the same as the standard. And you have a lot of it. You should declare victory and go into purification.
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