Originally Posted by eastshores
So the chemical composition of glutamic acid and monosodium glutamate (msg) are still not the same right? If I read correctly, it is the glutamic acid that gives us the ability to taste "umami".
Ok, some basic chemistry. Acids are substances that have protons which they like to shed. I.e. Hydrochloric acid HCl tends to react with water by forming Cl- ions, the excess proton being taken by the water to for a H3O+ ion. Add sodium (simplified here) and you get a mixture of Na+ ions and Cl- ions - salt water. Those ions do not really bond together, in solution, you do not get a NaCl compound, but just these individual ions floating around.
Same with glutamic acid. HOOC-CH2-CH2-CH(NH2)-COOH tends to shed that last proton in solution and ends up as HOOC-CH2-CH2-CH(NH2)-COO- , that is, glutamate. Commonly available as sodium glutamate, but the sodium does not really play a significant role. Our taste receptors like mGluR4 recognize the glutamate ion, not the free acid.
EDIT: Technically, in solution, you get the glutamate zwitterion -OOC-CH2-CH2-CH(NH3+)-COO- but that discussion probably leads too far.
2nd EDIT for failing at basic structural formulae.