The specific activity of a pure preparation of pyruvate kinase (PK) assayed in the direction of pyruvate formation (forward direction) is 220 U/mg at 25 C and at pH 7.5. This form of PK is a homotetramer (MW 240,000) with one active site per subunit. What is the kcat for PK in the forward direction?

The specific activity of a pure preparation of pyruvate kinase (PK) assayed in the direction of pyruvate formation (forward direction) is 220 U/mg at 25 C and at pH 7.5. This form of PK is a homotetramer (MW 240,000) with one active site per subunit. What is the kcat for PK in the forward direction?

Biochemistry

6th Edition

ISBN:9781305577206

Author:Reginald H. Garrett, Charles M. Grisham

Publisher:Reginald H. Garrett, Charles M. Grisham

Chapter26: Synthesis And Degradation Of Nucleotides

Section: Chapter Questions

Problem 14P: The Energy Cost of dTTP Synthesis (Integrates with Chapter 20.) Starting from HCO3, glutamine,...

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a. Compounds A, B, C, and D are known to be intermediates in the pathway for production of protein E. To determine where the block in protein-E production occurred in each individual, the various intermediates were given to each individuals cel Is in culture. After a few weeks of growth with the intermediate, the cells were assayed for the production of protein E. The results for each individuals cells are given in the following table. A plus sign means that protein E was produced after the cells were given the intermediate listed at the top of the column. A minus sign means that the cells still could not produce protein E even after being exposed to the intermediate at the top of the column. Draw the pathway leading to the production of protein E.
The enzyme glucose oxidase isolated from the mold Penicillium notatum catalyzes the oxidation of β-Dglucose to D-glucono-δ-lactone. This enzyme is highly specific for the β anomer of glucose and does not affect the α anomer. In spite of this specificity, the reaction catalyzed byglucose oxidase is commonly used in a clinical assay for total blood glucose—that is, for solutions consisting of a mixture of β- and α-D-glucose. What are the circumstances required to make this possible? Aside from allowing the detection of smaller quantities of glucose, what advantage does glucose oxidase offer over Fehling’s reagent for measuring blood glucose?
Mutants of Neurospora crassa that lack carbamoyl phosphate synthetase I (CPS I) require arginine in the medium in order to grow, whereas mutants that lack carbamoyl-phosphate synthetase II (CPS II) require a pyrimidine, such as uracil. A priori, one would expect the active CPS II in the arginine mutants to provide sufficient carbamoyl phosphate for arginine synthesis, and the active CPS I in the pyrimidine mutants to “feed” the pyrimidine pathway. Explain these observations.
For the following aspartate reaction in the presence of inhibitor, Km = 0.00065 M. Determine Vmax in both reactions and in the reaction without inhibitor, the Km. Identify whether the inhibition is competitive, non-competitive or uncompetitive. ( see attached picture ) how I and S bind to the E as shown by the Lineweaver Burk plot. the significance of the following obtained values for Km and Vmax. effect in slope and x-intercept
Pyridoxal phosphate (PLP) is a coenzyme for the enzyme ornithine aminotransferase. The enzyme was purified from cells grow in PLP = deficient media as well as from cells grown in media that contained pyridoxal phosphate. The stability of the two different enzyme preparations was then measured by incubating the enzyme at 37°C for different lengths of time and then assaying for the amount of enzyme activity remaining. The following results were obtained. (a) Why does the amount of active enzyme decrease with the time of incubation? (b) Why does the amount of enzyme from the PLP deficient cells decline more rapidly?
By analysis of the kinetics of interconversion of (1-13C]FBP and [6-13C]FBP and the appearance of 3-PGA and PEP in further experiments such as shown in the figure above, it was concluded that the rate of oxidation of glyceraldehyde-3-phosphate (GAP) was hindered under conditions of anaerobiosis. Separate experiments showed that the activity of 3-phosphoglcerate kinase was normaland that the concentrations of ADP and ATP were not limiting. What metabolic condition is the most likely to account for this conclusion? Write the reaction using structural formulas and naming reactants
The enzymatic activity of PFK1 is generally measured by set- ting up a coupled enzyme assay system whereby aldolase, triose phos- phate isomerase, and glycerol-3-phosphate dehydrogenase are added to the assay mixture. For the latter enzyme, NADH is added and its change in concentration is readily monitored at 340 nm. Write the chain of reactions catalyzed by these enzymes using structural formulas, label substrates and products, and explain why the coupled en- zyme assay system leads to oxidation of NADH. While the chain of reac- tions is similar to those in glycolysis, there is a critical difference because of the dehydrogenase enzyme. Describe how this enzyme causes the chain of reactions to differ from those in glycolysis.
The kcat and KM for chymotrypsin-catalysed cleavage of a synthetic substrate, S, were determined to be 60 s-1 and 0.5 mM, respectively, using steady-state kinetics. The concentration of enzyme in the assay was 5 x 10-8 M. ii) Draw a graph on the axes shown in Figure 1 below showing how the initial rate of the reaction varies with [S], making use of the values for KM and Vmax. Label the axes with appropriate titles and units.
The proximal histidine residues have been replaced by glycine residues by mutation of the cloned genes for both the α and β subunits of hemoglobin. With the tetrameric mutant hemoglobin (all subunits being mutant, α H F8 G, β H F8 G), it was found that the “proximal” coordination bonds to hemes in the mutant protein could be replaced by having the small molecule imidazole in the buffers. Oxygen binding curves for the tetrameric mutant hemoglobin were measured. A. The degree of cooperativity in oxygen binding for the mutant hemoglobin (with imidazole present) would be expected to 1) increase 2) decrease 3) not be affected) compared with the normal protein. B. Justify your answer to part A in terms of what you know about the structural basis of cooperativity in hemoglobin. C. How would the Hill coefficient for the mutant be expected to change compared with nH for normal hemoglobin, which is ~3?
Calculate the mass of invertase (in mg) and concentration of invertase (in mM) contained in a 25.0mL sample of yeast extract that has 3,000 total units of activity, assuming that pure invertase has a specific activity of 1,000 units/mg with a mass of 270kD.
At 37 °C, the serine protease subtilisin has kcat = 50 s-1 and KM = 1.4 × 10-4 M. It is proposed that the N155 side chain contributes ahydrogen bond to the oxyanion hole of subtilisin. J. A. Wells and colleagues reported (1986, Phil. Trans. R. Soc. Lond. A 317:415–423) the following kinetic parameters for the N155T mutant of subtilisin: kcat = 0.02 s-1 and KM = 2 × 10-4 M.(a) Subtilisin is used in some laundry detergents to help remove protein-type stains. What unusual kind of stability does this suggest for subtilisin?(b) Subtilisin does have a problem in that it becomes inactivated by oxidation of a methionine close to the active site. Suggest a way to make abetter subtilisin.(c) Is the effect of the N155T mutation what you would expect for a residuethat makes up part of the oxyanion hole? How do the reported values ofkcat and KM support your answer?(d) Assuming that the T155 side chain cannot H-bond to the oxyanion intermediate, by how much (in kJ/mol) does N155 appear to stabilize…
The Energy Cost of dTTP Synthesis (Integrates with Chapter 20.) Starting from HCO3, glutamine, aspartate, and ribosc-5-P, how many ATP equivalents are consumed in the synthesis of dTTP in a eukaryotic cell, assuming dihydroorotate oxidation is coupled to oxidative phosphorylation? How does this result compare with the ATP costs of purine nucleotide biosynthesis calculated in problem 2?