Case No. 128 · the exotic forty · have you seen this molecule?

Cadmium carbonic anhydrase

the diatom that runs on cadmium

File sealed

The detectives are still writing this one up. The poster and the facts are below; the film and the interrogation room open soon.

Booking photographs

Cadmium carbonic anhydrase, front view, against a height chart in nanometers — FRONT

Cadmium carbonic anhydrase, side view — SIDE · PDB 3BOB

The suspect, from its real atomic coordinates. Drag to turn it. Height chart in nanometers, ruled every 0.2 nm. The diatom that makes it is about three thousand times wider.

Rap sheet

Answers to: CDCA, to its friends.
Height: 5.0 nm, one of its three repeats.
Weight: 37 zeptograms, cadmium and all.
Build: One chain, disguised as a pair of an unrelated enzyme.
Marks: One cadmium atom in its active site. Trades it for zinc and back.
Habits: Turns carbon dioxide into bicarbonate and back, so a diatom can catch carbon.
Motive: Zinc is nearly gone from the sea. Cadmium is the stand-in.
Known for: Explaining why ocean cadmium tracks phosphate, like a nutrient.
Last seen: In diatoms in coastal seas, wherever zinc runs low.

2,200,000,000,000,000

cadmium atoms in a gallon of deep North Pacific water.
Near the top, something eats them. You’ve never seen it.

CASE FILE: Xu, Y. et al. (2008) Structure and metal exchange in the cadmium carbonic anhydrase of marine diatoms. Nature 452, 56–61.

The poster on the street

The wanted poster for Cadmium carbonic anhydrase

This is the photocopied wanted poster for Cadmium carbonic anhydrase, No. 128 of the exotic forty. They were made for noticeboards around Boston, Cambridge and the rest of the east coast.

Found one? Scan its QR code with your phone. If you're a signed-in player, the sighting goes on your record with +1 XP.

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