40
with L12 sUbstituted for V, the velocity of the catalyzed reaction. The
constant 5.2 x 10- 2 is the maximum value of L12 when the enzyme is saturated, and the constant 5.0 x 10- 3 is the half-saturation constant for
the enzyme (Bahr and Jensen,1974). The constant 5.2 x 10- 2 was obtained
by solving the equation -for standard growth conditions when the concentration of CO 2 was 10 ~m.
Since the chemical affinity of reaction 4, A 4 , is known, the 13
equations of the CO 2 -limited model may be solved for varying concentrations of CO 2 , the r e sults are shown in Figure 3. The response of the
model cells to limiting concentrations of CO 2 is approximately hyperbolic
and unlike light-limited growth, the cellular concentration of chlorophyll decreases with growth rate.
Both the quantum efficiency of photosynthesis and the chemical affinity for photosynthetic electron transport vary little, a s they did in light-limited growth. The decrease in
the phenomenological cross coefficient, L 12 , is an input into the model
and is caused by a decrease in substrate concentration. The concentration and specific activity of the rate limiting enzyme, ribulose 1,5diphosphate carboxylase, will remain constant. The cross coefficient
for coupling site 3-4, L 34 , decreases in parallel with chlorophyll content and specific growth rate.
3 •
I
!. i
I .
.. i .
, .
L
Figure 3. Responses to the concentration of carbon dioxide predicted by
the thermodynamic model. The responses
include specific growth rate,~, cel lu~
lar chlorophyll, ChI, catalytic capacity
at the two coupling sites, L12, and
L34, quantum efficiency, ¢, and the
chemical affinity of reaction 2, A 2 .
Referring again to Figure 1, we may summarize carbon-limited regulation as follows.
A decrease in carbon dioxide concentration will slow
reaction 1 because of a decreased conductivity. Since reactions 1 and
2 are coupled, reaction 2 will decrease, leading to a transient increase
in the chemical affinity of reaction 2.
In order to reestablish the
chemical affinity required for optimal efficiency of energy conversion,
the rate of coupled reactions 3-4 must decrease. This decrease is
achieved by decreases in both the chlorophyll content of the cells and
the conductivity at coupling site 3-4. Thus, cells in the new steady
state growth have a lower content of chlorophyll and lower levels of
enzyme activity. Although there are too few measurements of carbon-
with L12 sUbstituted for V, the velocity of the catalyzed reaction. The
constant 5.2 x 10- 2 is the maximum value of L12 when the enzyme is saturated, and the constant 5.0 x 10- 3 is the half-saturation constant for
the enzyme (Bahr and Jensen,1974). The constant 5.2 x 10- 2 was obtained
by solving the equation -for standard growth conditions when the concentration of CO 2 was 10 ~m.
Since the chemical affinity of reaction 4, A 4 , is known, the 13
equations of the CO 2 -limited model may be solved for varying concentrations of CO 2 , the r e sults are shown in Figure 3. The response of the
model cells to limiting concentrations of CO 2 is approximately hyperbolic
and unlike light-limited growth, the cellular concentration of chlorophyll decreases with growth rate.
Both the quantum efficiency of photosynthesis and the chemical affinity for photosynthetic electron transport vary little, a s they did in light-limited growth. The decrease in
the phenomenological cross coefficient, L 12 , is an input into the model
and is caused by a decrease in substrate concentration. The concentration and specific activity of the rate limiting enzyme, ribulose 1,5diphosphate carboxylase, will remain constant. The cross coefficient
for coupling site 3-4, L 34 , decreases in parallel with chlorophyll content and specific growth rate.
3 •
I
!. i
I .
.. i .
, .
L
Figure 3. Responses to the concentration of carbon dioxide predicted by
the thermodynamic model. The responses
include specific growth rate,~, cel lu~
lar chlorophyll, ChI, catalytic capacity
at the two coupling sites, L12, and
L34, quantum efficiency, ¢, and the
chemical affinity of reaction 2, A 2 .
Referring again to Figure 1, we may summarize carbon-limited regulation as follows.
A decrease in carbon dioxide concentration will slow
reaction 1 because of a decreased conductivity. Since reactions 1 and
2 are coupled, reaction 2 will decrease, leading to a transient increase
in the chemical affinity of reaction 2.
In order to reestablish the
chemical affinity required for optimal efficiency of energy conversion,
the rate of coupled reactions 3-4 must decrease. This decrease is
achieved by decreases in both the chlorophyll content of the cells and
the conductivity at coupling site 3-4. Thus, cells in the new steady
state growth have a lower content of chlorophyll and lower levels of
enzyme activity. Although there are too few measurements of carbon-