L-Glutamate tastes good (with tastebuds dedicated to its detection) because out of the available amino acids, the amount of glutamic acid in a mouthful is the one used by the gustatory system as a marker for protein. It has been estimated from average protein composition that humans are about 1% glutamate and have a flavour.
The first rule of Glutamine Club is that any high-glutamate food makes a good pizza topping.
That said, I have come to have doubts about marmite, and the Frau Doktorin was not well-pleased about the 'Avocado incident' of which we have agreed never to speak again.
natto. To say nothing of the fabled smutto.
Then we learned at Riddled Research Laboratory that glutamate has another role, not as a floor wax / dessert topping, but as "the most abundant excitatory neurotransmitter in the vertebrate nervous system". Enormous tracts of glutamergic nerves run between thalamus and cortex and all through the limbic system, easily recognised by anatomists because they trace out purple arrows.
Naturally our second thought was to extend this to other neurotransmitters. Inspired by the prospect of evolving new classes of tastebud for detecting serotonin and dopamine and GABA, we inveigled Greenish Hugh into the Evolvamat, pointing out the even more pretentious bollocks he would be able to spout in the Thursday night "Arthropod Tagmosis and Wine-tasting" sessions with the help of the additional flavours. Initial results from the tongue / brain parallel were promising...
...until we remembered that Greenish Hugh's tongue always looks like this, on account of that accident when a Shar Pei dog was trapped with him in the matter transmitter.
Our first thought, of course, was about the possibility of tasting foods by direct contact against extensions of the brain. It would be a valuable social accomplishment