BCHM 310 Lecture 34: BCHEM 315 12:2
22 Dec 2018
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Catalyses 1st step unique to pyrimidine biosyn (ctp, utp, ect) Two trimers of catalytic subunits, wedged inb/n are 3 regulatory subunits. 2 c3 and 3 r2 making a dodecamer (12 subunits) Allosterically inhibited by ctp and activated by atp. Helps to create a balance b/n purine + pyrimidine biosyn. Ctp + atp bind to the same site on the r subunits. Bases + size differ so can make diff h bonding interactions: trigger diff conformational states. Ctp binds to t state and atp binds to r state. Ctp is a -ve allosteric effector, atp is +ve allosteric effector. Ctp and atp are heterotropic allosteric effectors: dn bind to substrate binding site. Substrates are homotropic allosteric effectors affect their own binding sigmoidal curve. At low [s] mostly t state, low activity, if locked into t state get hyperbolic that dn reach vmax. At high [s] mostly r state, fully active, if locked into hypothetical r state would follow mm.
