A second Lineweaysr-Burk plot, this time for the substrate shikimate-3-phosphate

Question

A second Lineweaysr-Burk plot, this time for the substrate shikimate-3-phosphate, is shown below in Figure 4 from the study 5. Glyphosate (N-phosphonomethylglycine), which is better known as the successful, broad-spectrum, post-emergence herbicide 'Roundup', is a reversible inhibitor of the enzyme 5-enolpyruvyl shikimate 3-phosphate synthase (EC 2.5.1.19). This enzyme transfers the enolpyruvyl group from phosphoenolpyruvate to shikimate-3-phosphate to form 5-enolpyruvylshikimate-3-phosphate and inorganic phosphate (see reaction at the top of the next page). 10 EPSP Careful kinetic studies varying the concentration of one of the two substrates (the concentration of the other substrate was held constant) and the inhibitor glyphosate were conducted soon after this herbicide was first available. A Lineweaver-Burk plot for the substrate phosphoenolpyruvate is shown below in Fig. 3 from the study 0 0.2 0.4 0.6 0.8 1.0 shikimate-3-phosphate]-1 (u M) Fig.4. Effect of glyphosate on EPSP synthase: double reciprocal plot of initial velocity VS [shikimate-3-phosphate] at fixed 5.63 M PEP and glyphosate at: (O) 0; (.) 1 ??: (O) 2 ??; (4) 4?? 50 What type of inhibition is seen when phosphoenolpyruvate is the varied substrate (e.g., Fig 3)? (2 pts) a. 40 b. What type of inhibition is seen when shikimate-3- phosphate is the varied substrate (e.g., Fig. 4)? (2 pts) 30 Given these results and the fact that the authors provided evidence for a single displacement reaction mechanism, does the enzyme 5-enolpyruvyl shikimate 3-phosphate synthase appear to have an ordered or random bi bi reaction (1 pt) c. 20 d. Using Cleland notation, suggest the reaction sequence to form the ternary complex from phosphoenolpyruvate and shikimate-2-phosphate. Be sure to use the names of the real substrates and products! (2 pts) With an arrow, show to which form (or forms) of the enzyme in your answer to "d" above the inhibitor glyphosate binds. (1 pt) 0 0.02 0.06 0.14 e. PEPM' Fig.3. Effect of glyphosate on EPSP synthase: double reciprocal plot of initial velocity s [PEP) at fixed 177 ?? shikimate-3-phosphate and glyphosate at: (.) 0;

Explanation / Answer

1. Competitive inhibitor = All have same 1/Vmax
2. Uncompetitive inhibition - Both Vmax and Km change
3. Ordered
4. shikimate-3-phosphate + phosphoenolpyruvate ---EPSP synthase--- 5-enolpyruvylshikimate-3-phosphate (EPSP) + phosphate
5. Block the enzyme EPSP synthase.

Related Questions

Navigate

• Browse (All)
• Browse A
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.