down the rabbit hole towards 37C (/98.6F)

[mellowtigger]

Here's a good example of where my curiosity takes me.

1. It started with a pun on Mastodon, "Murder, She Roti".
2. What is roti? Oh, it's an unleavened bread.
3. What does that leave out? Various leavening agents.
4. Wait, there's a salt-leavened bread? No, that's a bad name, because there's no salt. It used to be stored in hot salt.
5. Wait, there's a bread that rises because of hydrogen instead of carbon dioxide? Yes, that bacterium is Clostridium perfringens.
6. Wait, that bacterium can cause a necrotizing disease, but people put it in their food?! Yes, but cooking destroys the bacteria to safe levels. Apparently. :/
7. If it's "safe", then how does it cause disease? It affects people who are protein deprived, which inhibits their trypsin production, which apparently deprives them of even more protein.
1. Wait, eating sweet potatoes does that too? Apparently so, unless you cook them well.
8. Why is trypsin important in the human body? Because trypsin begins the digestion process of protein molecules in the small intestine.
9. And... wait, what?! "Human trypsin has an optimal operating temperature of about 37 °C."?
1. That's the temperature for people living in the civilized world. For people in the USA, that's exactly 98.6 Fahrenheit.

So, I looked around and eventually found this publication.

Most hydrolyses have been reported at trypsin (EC 3.4.21.4) optimum conditions (pH 7.8 and 37 °C).

So... the obvious questions (and I haven't found any answers yet):

1. Is this molecule why humans evolved a body temperature of 37C/98.6F? If we deviate, then poor nutrition leaves us disadvantaged and subject to evolutionary culling?
2. What does this mean for our falling body temperature?
3. Other animals have different body temperatures (scroll upward to see the chart). Do they rely on some other process to kickstart their protein digestion?
1. I know humans have a weird intestinal digestion process, which is why we can't make use of the vitamin B12-producing bacteria that live in our gut. Other animals, however can use their own internally-hosted bacteria, so we eat their muscles, eggs, and livers to steal their bacteria-produced B12.
4. Are there some animals with the same temperature as humans, and do they have the same small intestine digestive process that we do?

Inquiring minds want to know.

Comments

[darkoshi]

Your mention of normal body temperature reminded me of this other thing I read.

https://siderea.dreamwidth.org/1778342.html
-> https://radiolab.org/episodes/fungus-amungus
(transcript)
...
MOLLY WEBSTER: And so what Arturo did was he got together with this mathematical biologist, Aviv Bergman, and first, they just gathered some numbers.

ARTURO CASADEVALL: What is the temperature susceptibility of fungi?

MOLLY WEBSTER: Like, most fungi don't like it above 86 degrees Fahrenheit.

ARTURO CASADEVALL: And then he looked at the well-known formulas for calorie use. And then he asked the question, if you put these two formulas together, what is the best temperature that keeps out most fungi but doesn't require you to have to eat all the time?

MOLLY WEBSTER: They basically crunched a number that had to do with, like, how many calories you need a day and, like, just, like, the energy that would take of eating and then keeping out pathogens.

ARTURO CASADEVALL: And what he found was that our temperature...

MOLLY WEBSTER: Ninety-eight-point-six.

ARTURO CASADEVALL: ...Is that temperature that best balances protection against the fungi versus the need to eat food.
...

Also discussed here: https://siderea.dreamwidth.org/1787739.html

[mellowtigger]

Thanks! That's so interesting. So many converging systems. :)

[armiphlage]

Or it could be the other way - our digestive system uses that molecule because it is compatible with our body temperature. If we had a warmer or cooler body temperature, our digestive system might have developed to use another enzyme.

Atlantic cod use a variant, trypsin Y. It has an optimal temperature of 21 C.

https://www.sciencedirect.com/science/article/abs/pii/S0308814608004238

I love how your mind works!

[mellowtigger]

Oh! I didn't think of the backward influence. Thanks for the idea. Yes, It's what I've repeated here many times over the years. "Everything is connected", which means that systems are very important. So many influences.

FWIW

[rebeccmeister]

Fun stuff!

Birds typically thermoregulate to 39 degrees C.

Most likely a large number of our enzymes have a thermal optimum at ~37 degrees C. This can change (on an evolutionary timescale) if our temperature setpoint changes.

I believe there are multiple hypotheses for why we thermoregulate to this temperature. I wouldn't discount the fungal disease hypothesis. There are probably some good energetics hypotheses, but I'm a bit skeptical of tracing the origins to digestive processes. My skepticism could be misplaced!