Download Pressure - People Server at UNCW

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(-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).
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.
Saturated acyl
chains, 1 atm.
Homeoviscous adaptation in marine
teleosts (Cossins and MacDonald, 1984).
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).
Pressure: Effects on Proteins
Volume changes in 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.
(Hochachka and Somero, 1984)
Polymerization/Subunit assembly:
Polymerization is entropically unfavorable –
often times water release to the bulk phase
drives these reactions (but this leads to V
increase).
Deep
Intermediate
Shallow
Pressure effects on LDH activity in 3 species of hagfishes with
different depths of occurrence. (Nishiguchi et al., 2008).
Shallow-living
Deep-living
Pressure (atm)
Effect of P on Km of NADH for M4-LDH in shallow- and deepliving 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?
Tradeoffs to the preservation of Km
T-P interactions and protein stability
Native
High T
High P
Low T
Low P
Effect of T and P on protein
denaturation. High T and High P
tend to denature proteins. Balny
et al. 1997.a
Denatured
Certain osmolytes stabilize/destabilize proteins
Concentrations of TMAO for
different fish and shrimp species
that were collected at different
depths (Yancey, 2001).
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).
Presumed mode of action of stabilizing and destabilizing solutes
High P
TMAO( )
TMAO( )
Urea ( )
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.
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).