‘Copper receptors in your nose are the reason you can’t escape garlic fingers. Hiroaki Matsunami, a molecular genetics professor at Duke University, told NYT Wirecutter that our olfactory system has an unusually high affinity for sulfur compounds — the same compounds that garlic releases when you crush or mince it. The chemical responsible is allicin, a sulfur-containing compound that binds directly to your skin and doesn’t wash off easily with soap and water.

The fix is chromium. Sulfur atoms are attracted to the chromium in stainless steel, so rubbing your hands on a stainless steel surface pulls the allicin compounds off your skin and onto the metal. Companies sell dedicated “stainless steel soap bars” for exactly this purpose, but any stainless steel object in your kitchen already does the same job. A spoon. A faucet. The inside of your sink basin.…’ (via Boing Boing)

The role of copper, referenced in the first sentence and never elucidated, is a genuinely fascinating piece of biochemistry. The reference is to the discovery that certain olfactory receptors responsible for detecting sulfur-containing compounds — thiols, like those released by garlic — are actually metalloproteins that require ionic copper as an essential cofactor. The copper isn’t incidental; it’s mechanistically central.

Here’s what the science shows: researchers discovered that the same receptors in the nose that pick up these unpleasant-smelling molecules also bind with particles of copper that reside in nasal mucus, and that this metallic binding partner amplifies the signal for the smelly molecules by up to 1,000 times. Scientific American

The confirmatory human work came in 2016: human thiol receptor OR2T11 responds specifically to gas odorants like ethanethiol and related low molecular weight thiols, and requires ionic copper for its robust activation — without it, the receptor loses almost all activity. ResearchGate

The structural basis is also becoming clearer: there is a highly conserved sequence in roughly three quarters of all olfactory receptors that constitutes a tripodal metal ion binding site, leading to the proposal that olfactory receptors are in fact metalloproteins — most likely with zinc, copper, and possibly manganese ions — that serve as a Lewis acid site for binding of many odorant molecules. Wikipedia

The evolutionary logic is elegant: we may have evolved our super-sensitive sulfur detection out of necessity, as those scents often signal the presence of rotten food, dangerous vapors, or unsanitary conditions. Ncdnadayblog The copper cofactor essentially acts as a signal amplifier tuned specifically to the sulfur–metal coordination chemistry that thiols naturally favor — which is why thiols were historically called mercaptans, from the Latin mercurium captans, “capturing mercury.”

There’s also a pleasing irony in the stainless steel spoon trick mentioned in the article: chromium in stainless steel pulls the sulfur compounds off your hands Boing Boing — another metal-sulfur coordination interaction, this time working in reverse, scavenging the very compounds that your copper-dependent receptors are so exquisitely sensitive to.

So “copper receptors” is compressed jargon for olfactory receptors that depend on copper ions as a cofactor for thiol sensitivity — a real and rather beautiful piece of metallobiology that the article cited correctly but left entirely unexplained.