Regulatory Strategies for Controlling Enzymes Flashcards
Allosteric Enzymes
•Binding at ____ site triggers _____ change that is _____ to the ____ ___.
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•Cooperativity - ___ at ___ ____ ____ ____ _____
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•2 Models
1.
2.
•Binding at regulatory site triggers conformational change that is transmitted to active site.
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•Cooperativity - action at 1 site affects other sites.
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•2 Models
1.Concerted
2.Sequential
Allosteric Models of Regulation
1.Concerted -
2.Sequential -
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1.Concerted - First binding changes binding in all sites
2.Sequential - Stepwise alteration of sites
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Aspartate Transcarbamoylase (ACTase) •Catalyzes the\_\_\_\_step in the biosynthesis of\_\_\_\_ giving rise to\_\_\_\_\_ nucleotides \_\_\_\_ \_\_\_\_\_\_(end product of the pathway)
•Catalyzes the first step in the biosynthesis of pyrimidines giving rise to pyrimidine nucleotides cytidine triphosphate (end product of the pathway)
ACTase Consists of Separable Catalytic and Regulatory Subunits
- ACTase consists of ___ ____ catalytic subunits and ___ ___regulatory subunits. (Quaternary structure)
- Each catalytic subunit consists of ___ chains, while the regulatory unit consists of ___ chains.
- The catalytic subunit and the regulatory subunits are held together by ____ _____ containing ___ ____residues bound to a ___ ion.
- ACTase consists of 3 large catalytic subunits and 3 small regulatory subunits. (Quaternary structure)
- Each catalytic subunit consists of 3 chains, while the regulatory unit consists of 2 chains.
- The catalytic subunit and the regulatory subunits are held together by stabilization domains containing four cysteine residues bound to a Zinc ion.
ATCase is Allosterically Inhibited and Activated
•At sufficiently high concentrations of CTP, ATCase is ____ by a end product feed back mechanism.
•The binding site for CTP is ___ from the ___ ____ of the enzyme. (____site). This site is found on the ____ subunit.
•High concentrations ATP acts as an allosteric ____.
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•At sufficiently high concentrations of CTP, ATCase is inhibited by a end product feed back mechanism.
•The binding site for CTP is distinct from the active site of the enzyme. (allosteric site). This site is found on the regulatory subunit.
•High concentrations ATP acts as an allosteric activator.
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ATCase Exists as Two distinct Quaternary Forms
- One predominates in the ____ of the substrate, while other predominates in the ____ of the substrate.
- T ____and R _____states.
- T state has ___affinity for the substrate and ___ catalytic power compared to the R state.
- One predominates in the absence of the substrate, while other predominates in the presence of the substrate.
- T (Tense) and R (Relaxed) states.
- T state has low affinity for the substrate and lower catalytic power compared to the R state.
Allosteric Regulators Modulate the T-to-R Equilibrium
•In the absence of substrate the R and T state are ____, however, the ___ is favored.
•In the presence of the allosteric inhibitor CTP, the position of equilibrium between the T and R states is shifted more towards the ___ state.
•This is a _____ mechanism (___ or ____) where ___ the subunits are converted to the ___state resulting in enzyme being___ ___ ___
•The R state is favored by ___ ___ and stabilized by ___ binding.
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•In the absence of substrate the R and T state are equilibrium, however, the T is favored.
•In the presence of the allosteric inhibitor CTP, the position of equilibrium between the T and R states is shifted more towards the T state.
•This is a concerted mechanism (all or nothing) where all the subunits are converted to the T state resulting in enzyme being completed turned off.
•The R state is favored by substrate binding and stabilized by ATP binding.
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Isozymes
- Enzymes of ____ amino acids sequences catalyzing the ____ reaction.
- These enzymes differ in ________ and _____
- Helps fine tune metabolic pathways within ___ ____
- Enzymes of different amino acids sequences catalyzing the same reaction.
- These enzymes differ in kinetic parameters (Km) and regulatory properties.
- Helps fine tune metabolic pathways within specific tissues.
Types of Covalent Modifications
______modification (______)
_______
_______
______
______ modifications (______)
______
_____
_______
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•Regulatory modification (reversible)
–Phosphorylation
–ADP ribosylation
–Acetylation
•Structural modifications (mostly irreversible)
-Glycosylation
-Lipid modifications
-g-Carboxylation of amino acid residue
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Covalent Modifications that Regulate Protein Activity
Phosphorylation
•Addition of a____ group to a protein.
•Enzymes that catalyze these reactions are known as___
•Serine and threonine are phosphorylated by _______________. (Example – Protein kinase A)
•Tyrosine is phosphorylated by_______
•Energy in the form of ___ is required.
•Dephosphorylation (removal of phosphate groups) is catalyzed by _____
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•Addition of a phosphate group to a protein.
•Enzymes that catalyze these reactions are known as kinases.
•Serine and threonine are phosphorylated by Serine/Threonine kinases. (Example – Protein kinase A)
•Tyrosine is phosphorylated by Tyrosine kinases.
•Energy in the form of ATP is required.
•Dephosphorylation (removal of phosphate groups) is catalyzed by Phosphatases.
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Ribosylation
•The enzyme_________________ transfers the _______ group from __________ onto ______________ residues.
•Bacterial toxins such as ____ toxin, ____ toxin, ____ toxin are ADP-ribosyltransferases.
•Diphtheria toxin catalyzes the ADP-ribosylation of _______ inactivating it and inhibiting protein synthesis.
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•The enzyme ADP-ribosyltransferase transfers the ADP-ribose group from Nicotinamide Adenine Dinucleotide (NAD+) onto Arginine, Glutamate or Aspartate residues.
•Bacterial toxins such as cholera toxin, pertussis toxin, diphtheria toxin are ADP-ribosyltransferases.
•Diphtheria toxin catalyzes the ADP-ribosylation of eukaryotic elongation factor-2 (eEF2), inactivating it and inhibiting protein synthesis.
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Acetylation
•Histone proteins are components of the ___ ___ ____
•_____ residues of histones are acetylated by _____ The enzyme that catalyzes this reaction is _______
•The process is reversed by _______
•Process regulates ___ ___
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•Histone proteins are components of the nuclear chromatin structure.
•Lysine residues of histones are acetylated by Acetyl-CoA The enzyme that catalyzes this reaction is histone acetyltransferase (HAT)
•The process is reversed by histone deacetylase (HDAC)
•Process regulates gene expression.
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Lipid Modifications
- Lipid molecules covalently bound to the _______ residues of proteins.
- Generally _____ ____ (____ and ____) or ____ ____ [____or _____-____(____groups) moieties] bind to proteins.
- Lipid molecules covalently bound to the N and C termini residues of proteins.
- Generally fatty acids (palmitate and myristate) or unsaturated lipids [farnsyl or geranyl-geranyl (prenyl groups) moieties] bind to proteins.
γ-Carboxylation
•Carboxylation of ______side groups.
•Found in the protein _____. (First ___ _______residues in the ___-terminus of the protein are carboxylated)
•g-carboxyglutamate is a stronger ___ ____ than glutamate.
•Binding of Ca2+ promotes Prothrombin to interact with the ____ enabling to be ___ ___ _____to enzymes that catalyzes it to the ___ ___ (____)
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•Carboxylation of glutamate side groups.
•Found in the protein Prothrombin. (First 10 glutamate residues in the N-terminus of the protein are carboxylated)
•g-carboxyglutamate is a stronger Ca2+ chelator than glutamate.
•Binding of Ca2+ promotes Prothrombin to interact with the membrane enabling to be in close proximity to enzymes that catalyzes it to the active form (Thrombin)
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