Biology Reference
In-Depth Information
Blackbody Radiation
Enzymic Catalysis
C
‡
E
5
E
4
C
n
E
3
C
i
E
E
E
2
C
3
E
1
C
2
E
0
C
1
Fig. 11.28 A comparison between
blackbody radiation
and
enzymic catalysis.
(
Left
) Blackbody
radiation involves promoting the energy levels (vibrational, electronic, or vibronic, i.e., both
vibrational and electronic) of oscillators from their ground state E
0
to higher energy levels,
E
1
-E
5.
The wavelength of the radiation (or quantum) absorbed or emitted is given by
D
E
¼
E
i
E
0
hf, where E
i
is the ith excited-state energy level, h is the Planck constant, f is the frequency,
and
D
E is the energy absorbed when an oscillator is excited from its ground state to the ith energy
level. Alternatively, blackbody radiation can be thought of as resulting from the transitions of
electrons from one energy level to another within matter, e.g., from E
1
to E
0
, from E
2
to E
0
, etc.
(
Right
) A single molecule of cholesterol oxidase (COx) is postulated to exist in n different
conformational states (i.e., conformers, also called
conformational substates
by Frauenfelder
et al. 2001), denoted here as C
i
with i running from 1 to n. Each
conformational state
(or
conformer
) is thought to carry a set of sequence-specific conformational strains, or
conformons
,
as explained in Fig.
11.20
and can be excited to a common transition state (denoted as C
{
)by
thermal fluctuations
¼
the skeleton of a
globular protein
, each covalent bond acting as an oscillator (with
vibrational frequencies in the range of 10
14
/s [Kurzynski 1997, 2006]) which, when
coupled properly, can lead to low-frequency
collective modes
of oscillations with
frequencies as low as 10
3
/s or less (according to the Fourier theorem [Herbert
1987]), thus accounting for the genesis of the so-called the slow protein coordinate,
X(t), of Prakash and Marcus (2007).
One crucial difference between
blackbody radiation
and
enzymic catalysis
is
thought to be this: Although both the
blackbody
and the
enzyme molecule
absorb
heat or energy from their environment (see the upward arrows in Fig.
11.28
) and
reemit it to their environment in equal amounts at equilibrium, what is experimen-
tally measured from these two systems is different: From the blackbody, the energy
reemitted is measured (see the blackbody spectrum in the upper right-hand corner
of Fig.
11.24
), while from COx, the disappearance of the fluorescence emission is
measured that results from enzymic catalysis, the
precondition of which being
energy absorption
(see the histogram in the upper left-hand corner of Fig.
11.24
).
