At first thought, a hemoglobin protein loaded up with CO molecules should have slightly less mass than an oxygenated hemoglobin complex, which could... theoreti

At first thought, a hemoglobin protein loaded up with CO molecules should have slightly less mass than an oxygenated hemoglobin complex, which could... theoretically... be measured, maybe with Raman spectroscopy. That effect is going to be tiny, though. Wikipedia is telling me a hemoglobin tetramer masses "about" 64,000 daltons, so a complex loaded up with 4CO will mass 64,111 vs 64,127 amu. 0.024% difference.