(A) Citrate Partly active carboxylase Inactive carboxylase Citrate (B) Dephosphorylated Highly phosphorylated 5 10 Citrate (mM) FIGURE 22.36 Dependence of the catalytic activity of acetyl CoA carboxylase on the concentration of citrate. (A) Citrate can partly activate the phosphorylated carboxylase. (B) The dephosphorylated form of the carboxylase is highly active even when citrate is absent. Citrate partly overcomes the inhibition produced by phosphorylation. [Information from G. M. Mabrouk, I. M. Helmy, K. G. Thampy, and S. J. Wakil. J. Biol. Chem. 265:6330-6338, 1990.] Acetyl CoA carboxylase activity

(b) ☐ The exergonic reactions catalyzed by isocitrate dehydrogenase (ICDH) and α- ketoglutarate dehydroge-nase (aKGDH) are regu- lated by metabolites, in addition to the reaction catalyzed by citrate synthase. The diagram to the right illustrates the activity of ICDH (A,▲) and aKGDH (O,●) in the presence of 1.5 mM ADP (O,A) or 1.5 mM ATP (●,▲). In muscle tissue contraction of sarcomeres initiated by a nerve im- pulse results first in the release of Ca 2+ from the sarcoplasmic reticulum. As indicated by the chang- es in velocity of the two enzymes, what are the flux changes of the TCA cycle in muscle tissue upon release of Ca2+ under the influence of ADP viz. ATP and under the influence of NAD+ viz. NADH on cit- rate synthase? 100 75 Stimulation of activity (% of maximum) ŏ 25 1. -8 -7 -6 log {[Ca2+] (M)}

In different organisms sucrose can be cleaved either by hydrolysis or by phosphorolysis. Calculate the ATP yield per mole of sucrose metabolized by anaerobic glycolysis starting with (a) hydrolytic cleavage and (b) phosphoro- lytic dleavage.

(b) the activity of the malate-aspartate shuttle (MAS) system of isolated rat brain mitochondria suspended in an isotonic me- dium buffered to pH 7.4. Diagram A illustrates NADH fluo- rescence emission upon addition of Glutamate in the ab- sence and presence of Aspartate. Diagram B illustrates sim- ilarly NADH fluorescence emission upon addition of Gluta- mate in the presence of Aspartate followed by additions of submicromolar concentrations of Ca2+. As is well estab- lished, the MAS in brain, skeletal muscle, and cardiac mus- Diagrams A and B on the right show changes in Glu A Glu В -No Asp + 0 +0.12 -0.48 + 16 0.81 +1.8 ++ Asp 10 min 2 min cle mitochondria is activated by cytosolic concentrations of Ca2* < 3 µM. To simulate the cytosolic part of the MAS, the following reagents were added to the medium: 4 units/ml glutamate-oxaloacetate transaminase, 6 units/ml malate dehydrogenase, 66 µM NADH, 5 mM aspartate, 5 mM malate, 0.5 mM ADP, 200 nM ruthenium red (to block the mitochondrial…