My peptide is a plant peptide and it's expressed in E.coli BL21
Check the sequence first. If you have very small peptide (less than 20) and have bulky side chains (Phe, Trp), you can try 280 nm absorption using theoretical extinction Molar (from ProtParam, Expasy). I'm reluctant to advise standard Bradford assay, Lowry is probably better choice (but then it depends on what solution your sample is in).
Ok, I am using Bradford to quantify my pure protein. I think I didn't explain very well. I would like do quantify the expression of my protein in a crude extract, because I 'll run 19 different conditions. I have used Elisa in another lab, but the problem is that I don't have the antibodies here. Then, I am looking for another technique that I can quantify only my peptide. My peptide has a histag. Thank you, Wangsa Ismaya.
If it's only for screening, I'd rather quantify it on gel (if possible). I don't know how big your peptide is (or protein? I'm confused).
For protein, I run known amount of protein standard (could be BSA or lysozyme, depends on the size you are targeting), for example 25 ng, 50 ng, 75 ng, 100 ng. For detection, at 100 ng we can visualize quite well with coomassie but lower than that is better use of silver staining. Next to them you can load 1 uL, 2uL, and 3 uL of your sample. The you can compare the density of your band. There are quantification programs or if not possible, the gel can be scanned and do quantification with (even) photoshop.
For a peptide, since you have Histag attached, I think you can do western blot against anti-His antibody. Quantification can be done with similar way as above (borrowed one of your colleague protein with Histag, with known amount)
It won't be precise but you can have at least a hunch on how much protein you have. For the sake of comparing you can even just compare the intensity of one band to another.
I hope it helps. Good luck.
Yes, I'm thinking on using SDS-PAGE. and the idea of using another protein to compare is very nice, I liked so much. This is a big peptide, that is why sometimes I call it protein. Thank you very much!
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