Pressure

1
Pressure

• Terrestrial environment constitutes lt1 of
  biosphere volume.
• Marine environment pressure ranges from lt1 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 CD/AB, ?G -RTlnKeq and v ks
• P sensitivity of reactions Kp K1e(-P?V/RT) and
  kp k1e-P?V/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).

2
Pressure Effects on Membrane Systems

• 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.

3
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).
4
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)
5
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).
6
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).
7
Pressure effects on LDH activity in 3 species of
hagfishes with different depths of occurrence.
(Nishiguchi et al., 2008).
8
Shallow-living
Deep-living
Pressure (atm)
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?
9
Tradeoffs to the preservation of Km
10
T-P interactions and protein stability
11
Certain osmolytes stabilize/destabilize proteins
12
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.
13
Are marine mammals sensitive to pressure?
Glycolytic flux in RBCs from marine and
terrestrial mammals during a 2 h incubation under
high hydrostatic pressure (Castellini et al.
2001).