Gp. Johari et G. Sartor, Water-ice equilibrium in hydrated proteins, and structural relaxation and H-bond equilibrium in a high protein food, beef, NUOV CIM D, 20(12BIS), 1998, pp. 2419-2435
Citations number
34
Categorie Soggetti
Physics
Journal title
NUOVO CIMENTO DELLA SOCIETA ITALIANA DI FISICA D-CONDENSED MATTER ATOMIC MOLECULAR AND CHEMICAL PHYSICS FLUIDS PLASMAS BIOPHYSICS
Configurational degrees of freedom available to the structure of most biopo
lymers in their native state further increase when the extent of their hydr
ation, particularly of proteins and nucleic acids, is raised, These allow w
ater and ice to coexist in the proteins below 273 K, and increase the distr
ibution of energy barriers for their structural relaxation. Hence, their vi
trification occurs over an extremely broad, almost indiscernible, temperatu
re range, as the configurational contribution to the thermodynamic function
s is lost gradually on their cooling. When annealed, a hydrated protein los
es part of its enthalpy and entropy spontaneously as certain of its H-bonde
d subunits and H2O molecules relax during the annealing period. The time an
d temperature dependence of the thermodynamics and kinetics of this process
of structural relaxation is studied by calorimetry of a native protein, be
ef, and mathematically formulated. A detailed analysis shows that at each t
emperature during the cooling of a hydrated beef sample, the native state o
f protein, the H-bond equilibrium becomes frozen-in, and that the frozen-in
equilibrium quotient increases on isothermal annealing, as the number of H
-bonds increases isothermally. The configuration contribution and the H-bon
ding contribution to the enthalpy and entropy become inseparable in biopoly
mers, as they should be for simpler materials, Description of both phenomen
a in general terms underscores the premise that simple model systems are no
t necessarily required for understanding the native protein's behaviour.