I'd be very skeptical that there is an actual biological mechanism that detects deuterium intentionally, there simply isn't really any need to this given that D

I'd be very skeptical that there is an actual biological mechanism that detects deuterium intentionally, there simply isn't really any need to this given that D2O is very rare. I'm not saying they don't exist, but there is no compelling argument why they would evolve. I'm not saying this can't exist, but I'd need some pretty convincing evidence that there's an actual biological reason for such a mechanism. But of course detection would be possible, it has been known for many decades that different isotopes change reaction kinetics (https://en.wikipedia.org/wiki/Kinetic_isotope_effect https://en.wikipedia.org/wiki/Kinetic_isotope_effect). That is a measurable chemical effect, so of course a protein could make use of it. This is something I was taught in university, so this is not any kind of obscure knowledge, but mainstream chemistry.