3. The investigators examined the behavior of the ATCase enzyme in the presence

Question

3. The investigators examined the behavior of the ATCase enzyme in the presence of CTP, and in the presence of both CTP and ATP. The concentration of CTP is 0.1 mM and the concentration of ATP is 2 mM. The results are shown in Figure 16.3. What is the significance of these observations?

A spartate transcarbamoylase (ATCase) catalyzes an early step in the synthesis of the pyrimidine nucleotides UTP and CTP. The enzyme catalyzes the condensation of carbamoyl phosphate and aspartate to form carbamoyl aspartate. The reaction pathway is shown in Figure 16.1. The enzyme has been fairly well characterized. It is known to consist of six regulatory subunits and six catalytic subunits. In this case, we examine the properties of ATCase isolated from E. coli to illustrate some of the important regulatory properties of multi-subunit enzymes. As an early enzyme in a multi-step pathway, the ATCase reaction is a logical one to regulate the synthesis of pyrimidine nucleotides. Both purine nucleotides and pyrimidine nucleotides are needed in roughly equal amounts as substrates for DNA synthesis in rapidly dividing cells. The regulation of the ATCase enzyme ensures a proper balance of purine and pyrimidine pools in E. coli. The goal in this case was to identify the cellular metabolites that serve as activators and inhibitors of ATCase.

Explanation / Answer

“ATCase” stands for Aspartate trans-carbamoylase enzyme. This enzyme is allosterically regulated. In allosteric regulation, an effector molecule binds to the enzyme into order to enhance its activity. The activity of ATCase enzyme is inhibited by high concentration of CTP molecule. The rate of the reaction or the catalytic activity of this enzyme is fast in the absence of high concentrations of CTP but decreases as the CTP concentration increases.

Hence, our graph significantly shows that the enzyme ATCase activity is low (i.e 30%) in the presence of only CTP (concentration of CTP high) whereas its activity is increased (i.e 80%) in the presence of both CTP and ATP (concentration of CTP low).

Related Questions

Navigate

• Browse (All)
• Browse 3
• Subjects

---

---

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