Chapter 25

What is the oxidation number of \(\mathrm{N}\) in nitrate, nitrite, \(\mathrm{NO}, \mathrm{N}_{2} \mathrm{O}\) and \(\mathrm{N}_{2}\) ?

How many ATP equivalents are consumed per \(\mathrm{N}\) atom of ammonium formed by (a) the nitrate assimilation pathway and (b) the nitrogen fixation pathway? (Assume for this problem NADH, NADPH, and reduced ferredoxin are each worth 3 ATPs.

Suppose at certain specific metabolite concentrations in vivo the cyclic cascade regulating \(E\). coli glutamine synthetase has reached a dynamic equilibrium where the average state of GS adenylylation is poised at \(n=6 .\) Predict what change in \(n\) will occur if: a. [ATP] increases. b. \(P_{11} / P_{110}\) increases. c. \([\alpha-\mathrm{KG}] /[\mathrm{Gln}]\) increases. d. \(\left[P_{i}\right]\) decreases.

How many ATP equivalents are consumed in the production of 1 equivalent of urea by the urea cycle?

Why are persons on a high-protein diet (such as the Atkins diet) advised to drink lots of water?

(Integrates with Chapter \(22 .\) ) Write a balanced equation for the synthesis of glucose (by gluconeogenesis) from aspartate.

Which vitamin is central in amino acid metabolism? Why?

Vitamins \(\mathrm{B}_{6}, \mathrm{B}_{12},\) and folate may be recommended for individuals with high blood serum levels of homocysteine (a condition called hyperhomocysteinemia). How might these vitamins ameliorate homocysteinemia?

People with phenylketonuria must avoid foods containing the lowcalorie sweetener Aspartame, also known as NutraSueet. Find the structure of Aspartame in the Merck Index (or other scientific source) and state why these people must avoid this substance.

Go to www.pdb.org and examine the pdb file 1 L.M 1 for glutamate synthase. Find its iron-sulfur cluster and FMN prosthetic group. Discover how this enzyme is organized into an N-terminal domain that functions in ammonia removal from glutamine (the glutaminase domain ) and the \(\alpha\) -ketoglutarate-binding site near the \(\mathrm{Fe} / \mathrm{S}\) and flavin prosthetic groups. Consult van den Heuvel, R. H. H., et al., \(2002 .\) Structural studies on the synchronization of catalytic centers in glutamate synthase. Journal of Biological Chemistry 277: \(24579-24583,\) to see how these two sites are connected by a tunnel for passage of ammonia from glutamine to \(\alpha\) -ketoglutarate.