Question

please answer a, b, and c. show all illustrations: graph and cleland notation

5. A protonated histidine residue in the active site of aspartate transcarbamoylase, ATCase, is thought to be important in stabilizing the transition state of the bound substrate a) Sketch a graph showing the pH dependence of the catalytic rate, assuming that this interaction is essential and dominates the pH-activity profile of the enzyme. Provide the biochemical basis for your graph. b) Identify one of the two substrates involved in the reaction catalyzed by ATCase and the enzyme class for ATCase. c) The ATCase mechanism is known to proceed via an ordered mechanism. Draw a Cleland notation diagram showing how this reaction proceeds. Abbreviate the second substrate as CP. Two products are formed.

answer a, b, and c please thank you

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Answer 1

Aspartate transcarbamoylase (ATCase) is a cytosolic enzyme that catalyzes the condensation of L-aspartate and carbamoyl phosphate (CP) to produce N-carbamoyl-L-aspartate (CAA). This reaction is the first committed step of the pyrimidine biosynthetic pathway. Cytidine triphosphate (CTP) and uridine triphosphate (UTP) are two end-products of pyrimidine biosynthesis. These compounds serve as cofactors in several metabolic reactions and are substrates in RNA synthesis. Subsequent modifications of these nucleotide triphosphates (NTPs) generate deoxy analogs for use in DNA synthesis.In mammals, ATCase forms part of the multi-enzyme complex CAD (alongside carbamoyl phosphate synthetase II and dihydroorotase) that catalyzes several steps in pyrimidine biosynthesis. Since pyrimidines are essential for DNA synthesis during cell division, ATCase inhibitors such as the transition-state analogue N-(phosphonacetyl)-L-aspartate (PALA) have the potential for slowing tumor growth in cancer. Allosteric regulation of ATCase by CTP and UTP prevents a pyrimidine surplus. These effectors synergistically inhibit ATCase activity, establishing a negative feedback loop. Conversely, adenosine triphosphate (ATP) and guanosine triphosphate (GTP) - both end-products of the parallel purine biosynthetic pathway - can act together to stimulate ATCase activity. Ultimately, the interplay between NTPs and ATCase ensures an appropriate balance of purines and pyrimidines within the cell.