Yes, theanine and glutamate are very similar, structurally. However, so are GABA and glutamate, and it's hard to have more polar opposite functions in the brain than those two.
What I'm trying to say is that minor differences in chemical structure can have enormous impacts on function. That said, it doesn't necessarily mean that they always *do*, so you may be on to something.
Indeed. My main point was about the taste - since they are so similar, it would make sense that both glutamate and theanine are considered the major components of the umami taste. They don't seem to be the exclusive source of the taste, but then L-Theanine does make up something like 50%-60% of the amino acid content in tea so it probably wouldn't taste any different if those others weren't present.
Tea also appears to have some protein content, which would be an obvious source of the taste as well.
IIRC, tyrosine is a dopamine precursor (it's what dopamine is made from), so it can help to restore proper dopamine levels in the brain. Where did the tyrosine thing come from, though?
Tea has Tyrosine
Most of what I've read has said that it helps you make better use of dopamine, but reports seem to vary.
It's not been proven to improve mood, but I suspect that anything that stimulates the brain helps to provide some temporary relief while it's working. So it may not do anything on a long-term basis, but I would suspect that it may have some contribution to the mood lifting effect that drinking tea can have.