pH Indicators and Fantastical Skin Colors
Ever since reading through the creative answers in this question
(How can I explain alien skin being different colors?)
I've been thinking about the logistics behind fantastical skin colors. However, one part that stuck out to me was the idea that pH levels could influence a creatures outward appearance.
One of the more promising things I found relating to that was bromothymol blue. Bromothymol blue is a pH indicator that has a range of colorless to bright blue, but with human blood levels would likely appear between tealy-green to muted turquoise. It is usually used to test amounts of carbonic acid, an element that already exists to some extent in human blood.
This leads me to main questions:
- How can a humanoid creature maintain this pH indicator in its physiology (as in, not immediately flushing it out of the system or dying of exposure)?
- How can I make the effects of the bromothymol blue manifest on the skin?
- As a bonus, are there any other chemicals that could work in a similar way and not require too many changes to human biology?
This post was sourced from https://worldbuilding.stackexchange.com/q/94205. It is licensed under CC BY-SA 3.0.
1 answer
What worries me about the bromothymol blue proposal is that it doesn't appear to be an organic chemical, i.e. no living organism produces it. This means that it's not possible (or at least unlikely) to be created in nature, and it would have to be artificially replenished. Those are obviously some big hurdles to overcome.
There are naturally-occurring pH indicators that serve just the way bromomythol blue does, for your purposes.
- Anthocyanins are synthesized in plants through the phenylpropanoid metabolic pathway in certain plants, using a number of enzymes. For this synthesis to work, an organism would in turn need to synthesize the enzymes used in this pathway. This is often a bit of a problem when it comes to introducing new chemicals into an organism: There are way more intermediate enzymes and proteins that are needed, and a delicate balance must be maintained. Still, it's not an impossible task - just a very difficult one. Anthocyanins are non-toxic to humans, so it shouldn't be a danger to your organisms.
- In Hydrangea macrophylla, the color of the flower is determined by levels of aluminum in the soil. Without aluminum, red anthocyanin dominates; when some sort of water-soluble aluminum compound is added, it can bind with the anthocyanin and turn the flower blue. To harness this, you'd want to look and anthocyanin production again, and determine how aluminum could get to the organism's cells (I'm assuming it would come through diet). Once again, you probably won't have toxicity issues.
- Litmus is the result of naturally-occurring compounds found in lichens. Unfortunately, it's a complex mixture when it works the best, but its properties are mainly due to a chemical called 7-hydroxphenoxazone, based in part on phenoxazine. I don't know whether a single organism could produce all of the constituent compounds.
I imagine that the main production centers of whichever indicator you choose would be near the top layers of the skin. Currently, special cells called melanocytes create melanin, which determines skin color. All you have to do is swap out melanocytes for whatever modified cells you design to create the pigments of your choice. They'll reproduce the pathways found in plant cells to produce the indicators, but that doesn't mean that they'll have all of the same features (e.g. cell walls) of plant cells. They'll be hybrids, really.
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