I have estimated Nitric Oxide from tissue homogenate by using griess reagent. From the standard curve, I got a concentration about 12 µM. I have used 100 µl of tissue homogenate. The protein concentration of my homogenate is 5 µg/ µl. I am a bit confused with the expression unit of Nitric Oxide. Should I express the concentration in terms of protein? What is the best way to express Nitric Oxide concentration in tissue? Thanks in advance.
I think it is important to express units with respect to protein levels because it reflects the relative activity of NO synthases, the level of which will vary between tissues. The absolute level of NO in tissue will of course be helpful in some regards. Having both will probably be helpful depending on the point you're trying to make.
If I want to express in terms of protein, then it comes 24 µM/ mg of protein.
Total protein I have taken 500 µg (100 µl X 5 µg/ µl). 24 µM/ mg of protein, is it proper way to express?
Since NO is a gas, and your assay is Griess for nitrite, it would not be too helpful to stretch the data and say that your data are robust enough to describe precisely how much NO **was** there. I would suggest you make comparison only between your control group and an experimental group. That way, you compare the relative changes in nitrite production (as a proxy of NO). Units become less of a concern.
To really accurately estimate NO levels in tissues, you would need much more sophisticated tools than Griess. Cheers.
If you really like to show the units, not the fold control. It should be nM/mg or uM/mg of protein in tissue lysate.
A minor point, but one that will confuse readers if not addressed, is that the symbol M is the abbreviation for molar or moles/L, and mol is the only abbreviation for mole that I am aware of. I'm not sure if others adhere to this rule or not, but units of nmol NO / mg protein make more sense to me than units of nM/mg protein.
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