[hapi001]

I am just have a biochemistry assignment, but i have no idea about it..
Would anyone mind to help me?


2.Describe the effect on the TCA cycle of :
a.increasing the concentration of NAD+,8%
b.reducing the concentration of ATP, and4%
c.increasing the concentration of isocitrate3%

[darko]

L.Stryer & other:Biochemistry:"The rate of the citric acid cycle is precisely adjusted to meet an animal cell's needs for ATP (Figure 17.18). The primary
control points are the allosteric enzymes isocitrate dehydrogenase and a-ketoglutarate dehydrogenase.
Isocitrate dehydrogenase is allosterically stimulated by ADP, which enhances the enzyme's affinity for substrates. The
binding of isocitrate, NAD+, Mg2+, and ADP is mutually cooperative. In contrast, NADH inhibits iso-citrate
dehydrogenase by directly displacing NAD+. ATP, too, is inhibitory. It is important to note that several steps in the cycle
require NAD+ or FAD, which are abundant only when the energy charge is low.
A second control site in the citric acid cycle is a-ketoglutarate dehydrogenase. Some aspects of this enzyme's control are
like those of the pyruvate dehydrogenase complex, as might be expected from the homology of the two enzymes. a-
Ketoglutarate dehydrogenase is inhibited by succinyl CoA and NADH, the products of the reaction that it catalyzes. In
addition, a-ketoglutarate dehydrogenase is inhibited by a high energy charge. Thus, the rate of the cycle is reduced when
the cell has a high level of ATP.
In many bacteria, the funneling of two-carbon fragments into the cycle also is controlled. The synthesis of citrate from
oxaloacetate and acetyl CoA carbon units is an important control point in these organisms. ATP is an allosteric inhibitor
of citrate synthase. The effect of ATP is to increase the value of K M for acetyl CoA. Thus, as the level of ATP increases,
less of this enzyme is saturated with acetyl CoA and so less citrate is formed."


hope it helps