Pressure•Terrestrial environment constitutes <1% of biosphere volume.

•Marine environment pressure ranges from <1 atm – 1100 atm.

•Average P of the ocean is 381 atm.

•High hydrostatic pressure impacts biological systems that undergo V changes.

•For a chemical/biochemical reaction:

•Keq = [C][D]/[A][B], G = -RTlnKeq and v = k[s]

•P sensitivity of reactions: Kp = K1e(-PV/RT) and kp = k1e-PV‡/RT

•P therefore affects both Keq and k.

•P effects occur at the organism, tissue, cell and molecular level.

•Gas-filled species are probably sensitive at all depths.

•Below about 500 m, small V have significant effects on G at the cell and molecular level.

•Membranes and cell-level systems are highly sensitive to P (HPNS).

Homeoviscous adaptation in marine teleosts (Cossins and MacDonald, 1984).

•High P leads to tighter packing of lipid membranes.

•This makes lipids more viscous and is analogous to the effect of low T.

•Also effects proteins that are embedded in the membrane as well as ion conductances.

Pressure: Effects on Membrane Systems

Saturated acyl chains, 1 atm.

Saturated acyl chains, high P

Unsaturated acyl chains, high P (homeoviscous adaptation)

Effect of P on the peak amplitude of action potentials in the vagus nerve of fishes from the deep-sea (open circles), mid-water (filled triangles) and shallow-water (filled circles). Forbes et al. (1986).

Effect of P on Na-K ATPase in membranes from gills of fishes.

Top: Deep living species are less affected by P than shallow living species.

Bottom: Activation volume is conserved at the adaptation P (dark line for each species). This implies that the membrane volume is also conserved.

Gibbs and Somero (1989)

Interaction of T and P in membrane processes.

Top: Na-K ATPase activity decreases at low T and at high P.

Middle: DPH Anisotropy (polarization) increases with increased P or decreased T (more ordered membrane).

Bottom: Correlation between Na-K ATPase activity (top) and membrane order (middle). The rate of the enzyme is directly related to membrane fluidity. From Chong et al. (1985).

Volume changes in proteins

(Hochachka and Somero, 1984)

Pressure: Effects on Proteins

Ligand binding: Charged/polar regions of active site and ligand have a hydration shell of densely packed water. Protein-ligand binding forces water into a less dense bulk phase (increased system V).

Protein conformational change:(1) Packing of amino acids in protein may change protein density.

(2) Hydration density changes result from exposure/burying of charged or polar amino acid residues.

Polymerization/Subunit assembly:Polymerization is entropically unfavorable – often times water release to the bulk phase drives these reactions (but this leads to V increase).

Pressure effects on LDH activity in 3 species of hagfishes with different depths of occurrence. (Nishiguchi et al., 2008).

Deep

Shallow

Intermediate

Effect of P on Km of NADH for M4-LDH in shallow- and deep-living species of teleosts all of which are adapted to similar T (-2 to 8 C) (Siebenaller and Somero, 1979). Note that Sebastolobus alascanus (open circles, 200-500 m) differs from S. altivelis (open squares, 600-1300m) by only 1 amino acid residue.Are cold-adapted species pre-adapted for life at depth?

Deep-living

Shallow-living

Pressure (atm)

Tradeoffs to the preservation of Km

Effect of T and P on protein denaturation. High T and High P tend to denature proteins. Balny et al. 1997.a

Low TLow P

High THigh P

Denatured

NativeT-P interactions and protein stability

Deep sea fish Km of NADH for LDH is raised by high P, but this effect is offset by the presence of TMAO (Gillett et al. 1997).

Certain osmolytes stabilize/destabilize proteins

Concentrations of TMAO for different fish and shrimp species that were collected at different depths (Yancey, 2001).

High P

TMAO( )

TMAO( )

Urea ( )

Presumed mode of action of stabilizing and destabilizing solutes

TMAO is preferentially excluded from the protein hydration layer (middle). This results in an entropy decrease, so the available protein surface area is minimized (protein is folded). Chaotropic agents like urea preferentially interact with protein surfaces (right), so the protein is unfolded to maximize the surface area for this favorable binding.

Glycolytic flux in RBCs from marine and terrestrial mammals during a 2 h incubation under high hydrostatic pressure (Castellini et al. 2001).

Are marine mammals sensitive to pressure?