91Ó°ÊÓ

Why is it in the muscle's best interest to export lactic acid into the blood during intense exercise?

Arsenate \(\left(\mathrm{AsO}_{4}^{3-}\right)\) closely resembles \(P_{i}\) in structure and reactivity. In the reaction catalyzed by glyceraldehyde 3 -phosphate dehydrogenase, arsenate can replace phosphate in attacking the energy-rich thioester intermediate. The product of this reaction, 1 -arseno3-phosphoglycerate, is unstable. It and other acyl arsenates are rapidly and spontaneously hydrolyzed. What is the effect of arsenate on energy generation in a cell?

Phosphofructokinase converts fructose 6 -phosphate to fructose 1,6 -bisphosphate, the committed step on the pathway that synthesizes ATP. However, some fructose 6 -phosphate is converted into fructose 2,6 -bisphosphate. Explain why depleting the substrate of PFK to form fructose \(2,6-\) bisphosphate is not a wasteful use of substrate.

Hexokinase in red blood cells has a \(K_{M}\) of approximately \(50 \mu \mathrm{M} .\) Because life is hard enough as it is, let's assume that the hexokinase displays MichaelisMenten kinetics. What concentration of blood glucose would yield \(v_{\mathrm{o}}\) equal to \(90 \% \mathrm{V}_{\max }\) ? What does this result tell you if normal blood-glucose levels range between approximately 3.6 and \(6.1 \mathrm{mM} ?\)

Glucose labeled with \(^{14} \mathrm{C}\) at \(\mathrm{C}-1\) is incubated with the glycolytic enzymes and necessary cofactors. (a) What is the location of \(^{14}\) C in the pyruvate that is formed? (Assume that the interconversion of glyceraldehyde 3-phosphate and dihydroxyacetone phosphate is very rapid compared with the subsequent step. (b) If the specific activity of the glucose substrate is \(10 \mathrm{mCi}\) \(\mathrm{mmol}^{-1},\) what is the specific activity of the pyruvate that is formed?