Control Mechanisms Flashcards
Course (coarse??) control?
Amount of enzyme present based on synthesis/degradation - slow
Fine control?
Activity of enzyme e.g. phos status, level in cell, substrate availability; rapid, can take ms
Passive control and MM kinetics?
Where at low S, V
Features of irreversible inhibitors and example?
Covalent modification
Often at active site, blocking S
Toxic
e.g. diisoprrpylphosphofluoridate, prototype of serine nerve gas which modifies a serine in the active site of acetylcholineesterase blocking action potentials
Reversible competition example?
Succinate dehydrogenase in citric acid cycle
Succinate – fumurate, inhibited by malonate
Can be overcome by high S
MM kinetics of each inhibition?
Irreversible: ? like removing the enzyme
Competitive reversible - Vmax same, Km up
Non-competitive reversible: Km same, Vmax down
Non-competitive reversible inhibition example?
Enzyme has both active and inhibitor sites, where I may prevent activity of S (without stopping it binding)
e.g. F16BP, gluconeogenesis by ATP
Feedback regulation in linear pathways?
End product controls rate of production
Avoids intermediate build ip
Stops unproductive over-production
Often reversible
Feedback regulation in branched pathways? (2)
2 or more end products needed in different amount, uses sequential feedback inhibition or nested feedback inhibition
Sequential feedback inhibition?
End product regulate intermediate step, often at branch point to cause linear inhibition of earlier bit
e.g. DAHP synthase in aromatic AA synthesis
Nested feedback inhibition
Both end products inhibit the first step, only for single regulatory enzymes with multiple inhibitor binding sites
e.g. purine biosynthesis
Control of mechanisms with multiple enzymes?
Nested feedback inhibition
Isoenzymes
What differs between isoenzymes?
Km
Cofactor requirements
Localisation
Genetic encoding
Examples of isoenzymes
Aspartokinase
Hexokinase
Allosteric regulators are all what?
Multi-subunit proteins, with multiple active sites
Homoallostery?
Co-operative substrate binding; 1 substrate (the ‘primer’) induces a conformational change to impact future binding potential
Gives sigmoidal kinetics e.g. haemoglobin
Heteroallostery?
Other effector molecules (not substrates) affect enzyme activity, either activating (stabilise active form) or inhibitors (stabilise inactive)
Regulation within a narrow S concentration range
Covalent modifications? ^)
Need energy; often in signalling pathways
Acetylation (of lysines)
Methylation (glutamate/aspartate)
Nucelotidylation (tyrosines)
ADP ribosylation (arginines)
Phosphorylation (OH group of serine, threonine, tyrosine)
Phosphorylation? Effects (4)?
Kinases and phosphates use phosphate group from ATP Ser + Thr - one class Tyr - second class Changes hydrogen bonds, negatively charges, affects 3D structure and S binding/catalysis
How do kinases recognise the residue?
Through consensus sequences - so as to avoid phosphorylating every AA that occurs
Nucleotidylation?
Addition of AMP = adenylation
UMP - uridylation
Used in biogenesis of organic nitrogen
First step in biogenesis of organic nitrogen?
Ammonia is assimilated into one of three pathways: carbamoyl phosphate, aspartate, or glutamate
Glutamate - glutamine regulation?
- Glutamate dehydrogenase catalyses reductive amination of alpha-ketoglutarate to form glutamate
- Second ammonia added to glutamate - glutamine via glutamine synthetase
Regulation of glutamine synthetase (GS)?
2 stacked rings of 6 subunits with 8 binding sites each for each inhibitor, of which all 8 must be present. (=96 effector sites in total)
Adenylation of Tyr397 near active site by AMP addition, forming an ester bond
