Figure 12.

Major mechanisms of thermoacidophily. (1) Thermoacidophiles have an inverted membrane potential with a positive charge on the inside of the cellular membrane and a negative charge on the outside to prevent the acidification of the cytoplasm by the passive diffusion of protons. (2) The inverted membrane potential is maintained by transporting cations such as K⁺ into the cytoplasm. (3) Cyclopentyl ring moieties on tetraether lipids increase packing of the tetraether lipids decreasing the permeability of the membrane by protons and increasing cellular heat stability. (4) Tetraether lipids make a monolayer that is less permeable to protons and more heat stable than diether lipids. (5) Proton pumps export protons from the cytoplasm to prevent the acidification of the cytoplasm. (6) Heat-damaged or protonated proteins can either be degraded via the proteasome or properly refolded by the thermosome.