English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

The allosteric control of aspartate transcarbamoylase (ATCase, EC 2.1.3.2) of Escherichia coli involves feedback inhibition by both CTP and UTP rather than just CTP alone. It has been known that CTP functions as a heterotropic inhibitor of catalysis; however, the inhibition by CTP alone is incomplete (50-70% at various aspartate concentrations) and there is only a partial occupancy of the allosteric binding sites by CTP at saturating concentrations. The logic of these allosteric characteristics can now be understood in that UTP is a synergistic inhibitor of ATCase in the presence of CTP even though UTP has no independent effect at pH 7.0. When saturating concentrations of CTP are present, the concentration of substrate required for half-maximal activity (S0.5) of the native holoenzyme for aspartate increases from 5 to 11 mM. When CTP and UTP are both present, the aspartate requirement increases further (S0.5 = 17 mM). At aspartate concentrations less than 5 mM, the heterotropic inhibition of ATCase is 90-95% in the presence of both pyrimidine nucleotides. UTP does enhance the binding of CTP to the holoenzyme but the number of tight binding sites does not change (n = 3). The binding of UTP is stabilized in the presence of CTP although its binding characteristics are not as strong as those of CTP. The recent crystallographic studies of Kim et al. [Kim, H.K., Pan, Z., Honzatko, R.B., Ke, H.M. &amp; Lipscomb, W.N. (1987) J. Mol. Biol. 196, 853-875] have described a structural asymmetry across the molecular two-fold axis that is consistent with these CTP/UTP interactions. The synergistic inhibition of ATCase by both CTP and UTP provides a satisfying logic for ensuring a balance of endogenous pyrimidine nucleotide pools.

In the presence of CTP, UTP becomes an allosteric inhibitor of aspartate transcarbamoylase.