Enzyme Regulation Flashcards
What is enzyme kinetics
Study of rate of enzyme catalyse reactions, and how the rate varies with different substrate concentrations/co factors/inhibitors/ metal ions/ ph
How does reaction rate vary with substrate concentration
First order at Low substrate conc,
Zero order at high substrate conc
What’s the michaelis menton reaction model, and what are three assumptions about it
E + S ES -k2-> E + P
- [S] > [E] so amount of substrate bound at any one time is small
- [ES] does not change with time. Formation of ES = breakdown of ES
- Initial velocities used, concentration of product small and back reaction can be ignored
What’s the michaelis menton equation, and what happens when v0= 0.5v max
V0= (Vmax[S])/(Km + [S])
Km= (K2 + K-1)/K1
When V0=0.5 Vmax, Km=[S]
When does Km represent substrate affinity?
When K2 is limiting (K2<
What is kcat?
Turnover number = number of substrate converted to product in a unit of time when enzyme is saturated with substrate
Lineweaver burke plot equation
1/V0 = (Km/{Vmax[S]}) + 1/Vmax
4 monomers of lactate dehydrogenase
H4, M4, H3M, H2M2, HM3
Is competitive inhibition reversible? Example
Yes
Malonate inhibition of succinate dehydrogenase
Examples of non competitive inhibition (reversible and irreversible)
Reversible: EDTA inhibits Mg2+ requiring enzyme
Irreversible: organophosphorus inhibition of cholinesterase
How do competitive inhibitors affect Km and Vmax?
Apparent Km is larger, Vmax remains the same
How do non competitive inhibitors affect Km and Vmax
Vmax is lowered, Km remains the same
How does angiotensin work? And what do ACE inhibitors do
Heart disease -> decreased tissue perfusion-> decreased renal flow-> decreased glomerular filtration-> reduced [Na] in distal tubule -> renin released -> angiotensinogen is converted to angiotensin 1(by cleavage between L & L) -> ACE converts angiotensin 1 to angiotensin 2 (cleavage between (H & F) ->
Aldosterone release-> water reabsorption-> oedema
Peripheral vasoconstriction
Increased blood volume-> high bp-> heart disease
ACE inhibitors inhibit ACE
What’s an acetylcholinesterase inhibitor?
inhibits the acetylcholinesterase enzyme from breaking down acetylcholine
Used in Alzheimer’s
How Is enzyme activity regulated
- Allosteric binding sites
- Covalent modification
- Induction or repression of enzyme synthesis
What effect do allosteric enzymes have on the reaction velocity VS [S] curve? Positive effectors vs negative effectors
Examples
Normal enzymes show hyperbolic curve
Allosteric enzymes show a sigmoid curve.
Positive effectors bind outside active site and make it more complementary to substrate
Negative effectors bound outside active site and make it less complementary to substrate
-ve: ATP and citrate on phosphofructokinase
+ve: phosphoenolpyruvate (PEP) and fructose 1,6 bus phosphate on pyruvate kinase
Allosteric regulation of phosphofructokinase
Fructose 6 phosphate is converted by phosphofructokinase to fructose 1,6 bisphosphate
AMP activates the inhibited PFK
ATP/ citrate inhibits PFK
Allosteric regulation of pyruvate kinase
PEP is converted to pyruvate by pyruvate kinase.
Fructose 1,6 bisphosphate and PEP are positive effectors
5 methods of covalent modification
- Phosphorylation
- Adenylylation
- Uridylylation
- ADP-ribosylation
- Methylation
What happens in phosphorylation and dephosphorylation?
Phosphorylation may result in increased/decreased activity
Addition /removal of phosphate from S/T/Y/H
Increased activity of glycogen phosphorylase by phosphorylation by phosphorylase kinase serine 14
Dephosphorylation by phosphorylase phosphatase
Phosphorylation at ser residues by glycogen synthase kinase 3-> Decreased activity of glycogen synthase
Dephosphorylation by phosphoprotein phosphatase
Phosphorylation at several Ser residues (by glycogen synthase kinase 3) inactivates enzyme
Dephosphorylation by a phosphoprotein phosphatase
How blood glucose levels regulate enzymes
High blood glucose-> elevated insulin-> increased synthesis of glucokinase/ phosphofructokinase / pyruvate kinase
