concept

Piezolyte

Small zwitterionic organic molecules that deep-sea organisms accumulate to keep pressure from unfolding their proteins — principally trimethylamine N-oxide, TMAO. The mechanism is subtle: TMAO is excluded from a protein's immediate hydration shell, and that exclusion thermodynamically favours the folded state. In marine bony fish, muscle TMAO rises almost linearly with depth, correlating at about 0.94. That linearity is the trap: teleost blood is dilute relative to seawater, so the rising line crosses the sea's 1,100 mOsm/kg somewhere around 8,200–8,400 m — which is precisely the depth below which bony fish are no longer found.