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Unformatted text preview: is sufficient for the needs of
the cell, CTP inhibits an enzyme that catalyzes an early step in the synthetic pathway, ATCase, by feedback
(d) ATP is a positive effector because when ATP is added the affinity of the E for the S increases. This is
indicated by the decrease in K0.5 in the presence of ATP.
(e) One reason, there may be other reasonable ideas: ATP is a purine nucleotide whereas CTP is a pyrimidine
nucleotide. Activation of ATCase by ATP promotes CTP synthesis when [ATP] is high thus balancing the
cellular pool of purine and pyrmidine nucleotides....
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- Winter '13