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UKCD Biochem Lec 9

Terms from Biochem lecture 9

Regulatory Strategies Allosteric control - binding substrate causes conformational control, activator or inhibitor, Multiple forms of enzymes, Reversible covalent modification, Proteolytic activation
ATCase Allosteric Regulation, ATCase catalyzes the first step in pyrimidine synthesis. 6 regulatory subunits and 6 catalytic subunits, Tetrahedral transition state likely
CTP inhibits ATCase, structurally different from the substrates, CTP must bind to a different site in ATCase
PALA is a potent inhibitor of ATCase and binds very tightly
T state inactive
R state active
concerted transition the conformational change is “all or none”
concerted mechanism binding of substrate induces all subunits to adopt the R state, binding CTP pushes all subunits towards the T state
sequential mechanism there are intermediate states in which some subunits are in the T state and some are in the R state, negative cooperativity
homotropic undergoes substrate-induced allosteric interactions
heterotropic ATP/CTP-induced allosteric interactions
Hemoglobin is made up of four subunits - 2 α-subunits and 2 β-subunits, oxygen-bindingcapacity is due to a prosthetic group bound by each subunit - the heme, Four oxygens can be bound - one per subunit
cooperative binding Binding one oxygen pushes the interface towards the R state, making it easier to bind a second, and so on
Bohr effect H+ and CO2 promote hemoglobin release of oxygen
carbamates CO2 reacts with the terminal amino groups
Isozymes enzymes differ sequence catalyze same reaction, coded separate genes via gene duplication/divergence, display diff kinetic behavior, diff substrate affinities, or regulated in different manners, fine-tuning of processes by using different amounts of each
Covalent Modification attachment of a molecule to an enzyme (or other protein) can alter its activity, reversible or irreversible
Protein kinases catalyze addition of phosphoryl group
multifunctional kinases they phosphorylate many different targets
Dedicated kinases phosphorylate a single protein or family of closely related proteins
Protein phosphatases catalyze removal of phosphoryl group
PKA phosphorylates specific serines and threonines, activated by cAMP, two kinds of subunit: two large regulatory subunits (R) and two smaller catalytic subunits ©
pseudosubstrate sequence look like the real sequence
zymogens inactive precursors, activated by proteolytic cleavage occur outside cell
Cleavage of a specific peptide bond activates the enzyme
Trypsin enteropeptidase, is the common activator of all the pancreatic zymogens
Oxyanion hole stabilizes the tetrahedral transition state
specific protease inhibitors Need different mechanism to turn off proteolytic enzymes
Blood clots are formed by a series of zymogen activations a cascade: leads to large amplification
Intrinsic pathway results from rupture of blood vessels
Extrinsic pathway results from tissues releasing clotting substances in response to trauma
serpins serine protease inhibitor, antithrombin III, plasmin
Heparin increases the rate of formation of complexes of antithrombin with the clotting serine proteases – anticoagulant
Plasmin formed by proteolytic activation of plasminogen, an inactive precursor. This is carried out by tissue-type plasminogen activator (TPA), another serine protease
Trypsin cleaves peptide bond
π-chymotrypsin cleaves other π-chymotrypsin molecules to form α-chymotrypsin.
The three chains of α-chymotrypsin are connected by two disulfide bonds
Created by: wiechartm