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Thursday, 13 January 2011
Bitter is the taste of poison. Almost all toxic substances taste bitter to some extent. And some things - particularly some harmless plants - taste bitter even though they are not poisonous. This is for the same reason that a harmless hover fly looks like a wasp. The plant has evolved a bitter taste after animals that might eat it evolved to flag up poisons using their sense of bitterness. Think cabbage; think coffee.
Children don't eat their greens because they are very sensibly resisting their mad parents' attempts to poison them. Parents do eat their greens because they have learned that they get sustenance (or - more immediately - a caffeine hit) by overcoming their initial revulsion. Indeed, most adults have conditioned themselves actively to like bitter - coffee and pink gin are treats.
But if such a diverse range of chemicals all give rise to the same taste, that must surely mean that there are receptors on our tongues for all those many different molecules? Most poisons work by binding to some specific vital body protein and so stopping it from doing its job. Maybe the way that evolution has designed the bitter area of our tongues is simply to take all (or a lot of) the proteins that - if blocked - would stop us from working, and to wire a small sample of each one in our taste buds into the one bitter signal to our brains.
Now most drugs work in the same way as most poisons - they bind to specific proteins to slow or to stop their function. Indeed, many drugs are poisons if taken in super-medicinal doses. And most drugs taste bitter.
Perhaps an easy way to find lots of useful new drugs would be to find just those proteins wired into our bitter taste buds, and then look specifically for substances that bind to them.