5. Many years later, in 1989, Wild, et al. revisited the idea of allosteric cont
ID: 165228 • Letter: 5
Question
5. Many years later, in 1989, Wild, et al. revisited the idea of allosteric control of ATCase by CTP. They noted that CTP did indeed inhibit ATCase, but that the inhibition was always incomplete, even at high concentrations of CTP. They hypothesized that perhaps CTP did not act alone, but in combination with some other nucleotide. They tested the activity of ATCase in the presence of several nucleotide combinations. The results are shown in Table 16.3.
a. What combination gives the most effective inhibition?
b. What is the physiological significance of this combination?
c. Revise Figure 16.1 to include this new information.
d. Redraw Figure 16.2 to include this new information. How does the KM of the nucleotide combination compare with the values for the nucleotides alone?
CASE 16 Allosteric Regulation of ATCase Table 16.1: Names and Abbreviations of Nucleic Acid Bases, Nucleotides and Nucleosides. (Based on Voet and Voet, 1995. Nucleotide Base formula Nucleoside Nucleotide Base I X H X ribose Nucleotide X ribose X deoxyribose OH triphosphate X ribose triphosphate phosphate AMP dATP ATP Adenine Adenosine dGTP Guanine Guanosine GMP GTP dCTP Cytosine Cytidine CMP CTP UTP NH Uracil Uridine UMPExplanation / Answer
Q.No 1
The combination of CTP and UTP gives most effective inhibition than compared to others. These combination shows 95% of the ATCase activity, which is inhibited by adding CTP and UTP. Whereas, the inhibitory effect should be varied, because CTP alone only 70% of ATCase activity and UTP alone shows 5% of ATCase activity.
Q.No 2
UTP and CTP both are comes under pyrimidines. CTP is always synthesized from UTP and the regulation of the ATCase creates metabolic sense, which can produce large quantity of CTP. After production of CTP inhibits ATCase enzyme, but not inhibit in a complete manner. When UTP level increase, this CTP and UTP will act synergistically and completely inhibit the ATCase enzyme.
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