39
or catalytic capacity of the cells.
In light-limited growth where the
concentration of nutrients remains constant, decreases in L12 and L34
with decreases in irradiance reflect decreases in either enzyme concentration or specific activity at both coupling sites.
Looking at Figure 1, we summarize the metabolic regulation by
phytoplankton required for light-limited growth as follows.
A decrease
in irradiance will slow reaction 4, which will slow reaction 3 because
they are tightly coupled. A decrease in reaction 3 will lead to a
transient decrease in the chemical affinity of reaction 2.
In order to
reestablish the chemical affinity required for optimal efficiency of
energy conversion, the rate of reactions 1 and 2 must decrease with
respect to reactions 3 and 4.
This is achieved by decreasing the conductivity at both coupling sites and increasing the chlorophyll content
of the cells. Such alterations in enzymatic activity and capacity for
gathering radiant energy are consistent with the observations on Chlorella by Hyers and Graham (1971).
The observations are also consistent
with Bjorkman's (1968) observation that the enzyme ribulose 1,5-diphosphate carboxylase is found in much lower concentration in shade plants
than in sun plants.
IV. PREDICTIONS FOR CARBON·- LUlITED GROWTH
According to the phenomenological equations (eqs. 4-7), fluxes are
affected by either variations in the phenomenological coefficients or
by variations in chemical affinities.
In the system described by Figure
1, decreases in CO 2 concentration may cause a decrease in the chemical
affinity of reaction 1 (see equation 2) or a decrease in phenomenological
coefficients, Lll and L 12 · The decrease in coefficients is a much more
important factor in regulation than the decrease in chemical affinity.
In order to describe carbon-limited growth, we again invoke equations 3-14, which describe light absorption, electron flow, constant
degrees of coupling, and optimal efficiency in energy conversion. The
empirically-derived relationship, 15a, is however replaced by:
-2
5.2xlO
(C0 2 )
-3
5.0xlO +(C0 2 )
(15b)
This equation describes changes in the phenomenological cross coefficient
with changes in carbon dioxide concentration.
It is assumed that the
enzyme ribulose 1,5-diphosphate carboxylase is the rate limiting enzyme
for carbon-limited growth, and that variations in Ll2 are caused by an
insufficient concentration of CO 2 to saturate the enzyme.
The equation
is of the form of the Michaelis-Menten equation for enzyme kinetics
or catalytic capacity of the cells.
In light-limited growth where the
concentration of nutrients remains constant, decreases in L12 and L34
with decreases in irradiance reflect decreases in either enzyme concentration or specific activity at both coupling sites.
Looking at Figure 1, we summarize the metabolic regulation by
phytoplankton required for light-limited growth as follows.
A decrease
in irradiance will slow reaction 4, which will slow reaction 3 because
they are tightly coupled. A decrease in reaction 3 will lead to a
transient decrease in the chemical affinity of reaction 2.
In order to
reestablish the chemical affinity required for optimal efficiency of
energy conversion, the rate of reactions 1 and 2 must decrease with
respect to reactions 3 and 4.
This is achieved by decreasing the conductivity at both coupling sites and increasing the chlorophyll content
of the cells. Such alterations in enzymatic activity and capacity for
gathering radiant energy are consistent with the observations on Chlorella by Hyers and Graham (1971).
The observations are also consistent
with Bjorkman's (1968) observation that the enzyme ribulose 1,5-diphosphate carboxylase is found in much lower concentration in shade plants
than in sun plants.
IV. PREDICTIONS FOR CARBON·- LUlITED GROWTH
According to the phenomenological equations (eqs. 4-7), fluxes are
affected by either variations in the phenomenological coefficients or
by variations in chemical affinities.
In the system described by Figure
1, decreases in CO 2 concentration may cause a decrease in the chemical
affinity of reaction 1 (see equation 2) or a decrease in phenomenological
coefficients, Lll and L 12 · The decrease in coefficients is a much more
important factor in regulation than the decrease in chemical affinity.
In order to describe carbon-limited growth, we again invoke equations 3-14, which describe light absorption, electron flow, constant
degrees of coupling, and optimal efficiency in energy conversion. The
empirically-derived relationship, 15a, is however replaced by:
-2
5.2xlO
(C0 2 )
-3
5.0xlO +(C0 2 )
(15b)
This equation describes changes in the phenomenological cross coefficient
with changes in carbon dioxide concentration.
It is assumed that the
enzyme ribulose 1,5-diphosphate carboxylase is the rate limiting enzyme
for carbon-limited growth, and that variations in Ll2 are caused by an
insufficient concentration of CO 2 to saturate the enzyme.
The equation
is of the form of the Michaelis-Menten equation for enzyme kinetics