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I'm starting for protein expression analysis.
In gene expression, we have TPM, RPKM etc. However, all I can see for protein expression is: "High", "Medium", "Low" and "Not detected".
Q: Is there a unit for measuring protein expression like gene expression? I've seen people talking about PE (protein existence). Can we use it for protein expression?
I would guess that the real unit for measuring protein expression would be pM (pico-moles) or a count of protein molecules.
I'm not sure we have any methods to calculate such quantities though.
The unit of measurement in protein expression is more or less "abundance". In mass spec this is derived from the area under the curve in the spectrum. In things like an ELISA this is derived from a color intensity.
Protein existence is a vague summarization of multiple data sources to try to quantify the likelihood of a protein existing. You can't use that for expression, though expression would influence the likelihood of existence.
