This is a bit of a cheat. I try to blog a day in advance, but of course yesterday was Monday, the day after maid’s day off, so I had to write Monday’s blog, then my next blog. For reasons that will become clear tomorrow, I had to write Wednesday’s blog yesterday as well as Monday’s, which meant that Tuesday’s blog, ie the one for today, got neglected. So I had to drag Tuesday’s blog, today’s, out of the B Warehouse, which is where I store blogs I’ve written but not yet blogged. I do hope that’s all clear.
Sad to relate, you can’t see in the dark. To see, you require light. But there are some interesting ways of finding this requirement. By a strange coincidence somebody put a post up on Facebook a few of days ago about angler fish. These ugly little suckers attract their prey by means of a ‘fishing rod,’ a bodily protuberance that has a lure on it. In deep dark waters, the lure luminesces, and prey are attracted by the light. Then they get eaten.
What was odd was that, when the post rolled in, I happened to be looking for some information on luciferases, since I thought this might make an interesting blogpost. Spooky, eh?
Luciferases are enzymes found in bioluminescent organisms that allow them to turn metabolic energy into light without any heat being evolved. There’s more than one, depending on the source. That found in fireflies is similar to that found in click beetles. In turn it’s different from those found in sea pansies, or bacteria, or dinoflagellates, or marine copepods. That’s odd too. Lots of ways of achieving the same evolutionary aim. You’d think it was wasteful, but Nature thinks it’s a damned good idea, this parallel evolution malarkey.
Copepods are little crustaceans, a bit like but not the same as krill (staple diet of the baleen whales as I’m sure you are aware,) and their luciferases are a bit different from those found elsewhere. They’re actively secreted and don’t remain inside the synthesising organism. That means you can do lots of different tests on copepod luciferases from the same organism because you don’t need to mash it up. Most of the glow in the wake of a ship at night, or in waves breaking on a beach, comes from copepods, but there’s some from other things such as jellyfish.
I knew all of this because at university I did a literature research project on luciferases. This was before I got sidetracked onto training goldfish http://wp.me/p2C8Zz-vu. It still fascinates me all these considerable years later.
Then I got to thinking about GlowSticks, so beloved of urban warrior ravers, and indeed of professionals needing light without heat, such as in areas where there may be pockets of inflammable gas or vapours and you really don’t want any danger of a spark from anything electrical. Deep sea divers use them too. Do they work the same way, I wondered? Well, yes and no.
Both bioluminescence and GlowSticks rely on the oxidation of a molecule. In animals this is a flavine of some description, of a group called luciferins, and they will not oxidise without a luciferase enzyme. They emit photons as the oxidise, hence the glow. (It’s a bit more complex than that, but I’ll not bore you.) In a GlowStick, you drop a couple of Es and then you break the glass capsule in the plastic tube before you start pulling shapes and yelling ‘Aceeeedddd!’, just before being hospitalised for hyperthermia and dehydration. When you break the capsule, you release some hydrogen peroxide into the tube containing a phenyl oxalate ester (no, don’t ask, you really do not want to know,) and the ester oxidises. It fires off photons as it does so, but sadly these are not in the visible spectrum. They have to interact with a fluorescent dye, which absorbs the photons and re-emits them at a visible wavelength, just like a high vis safety jacket. The colour of the fluorescent dye determines what colour it glows.
Mildly interesting snippet. If you activate a GlowStick and pop it in your freezer, it will stop glowing. Bring it out and let it warm up, it will start glowing again. But only till the reagents are exhausted. Then it’s all over. It’s a dead GlowStick. Awwwww.
One last point. A cat’s eyes do not glow in the dark. They glow in very dim light because the retina is partly reflective, and the light bounces around inside the eye so the cat can make the most of this precious hunting resource. It doe mean their visual acuity isn’t great, but there’s a price to pay for everything. A cat’s eyes do not glow in the dark, hence you can’t find a black cat in a dark cellar, a proverbially difficult task.