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bis102-11-14 - substrate is required to attain a given...

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ni - 2 types of subunits: catalytic and regulatory - can dissociate these subunits from one another by reducing the disulfide linkage between the cysteine linkages and then separate them by ion-exchange chromatography... -isolated catalytic subunit- has enzyme activity. follows michaelis-menten kinetics -isolated regulatory subunit- doesnt have enzyme activity. binds CTP -can reconstitute the native enzyme by combining the isolated subunits. the reconstituted enzyme has the same sigmoidal kinetics as the native enzyme. like hemoglobin, ATCase exists in an equilibrium of two forms, the T form and the R form. T state (less active) R state (more active) --pink -- regulatory subunits (pink) hold the catalytic subunits (yellow) CTP binding to the regulatory subunits helps stabilize the T state of the enzyme. T state- favored by CTP binding R state- favored by substrate binding CTP is a negative effector and increases the initial phase of the sigmoidal curve. more
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Unformatted text preview: substrate is required to attain a given reaction rate. The organism needs a balance of purines and pyrimidines ATP - acts as a positive effector of ATCase and helps cell maintain a balance of CTP and ATP Allosteric regulation of enzymes is noncovalent regulation of enzymes Covalent regulation of enzymes-covalent addition or removal of a molecule to an enzyme can also modify its activity. most of these modifications are reversible ex: phosphorylation and dephosphorylation enymes catalyzing phosphorylation reactions are called protein kinases -- can enable the regulation of an enzyme to be fine tuned according to a specific substrate, tissue or time of development. Protein kinase A recognizes the following consensus sequences: RRXSZ or RRXTZ S or T is the site of phosphorylation X is a small residue (either glycine or alanine) Z is an amino acid with large hydrophobic R group ( trp or phe)...
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