FHMP 012 enzymes in medicine Flashcards
what are the differences in fast and slow enzyme regulation
slow =
- hours/days
- in response to hormones like steroid or long term adaptations
- transcription rate
- mRNA stability
- Translation rate
- Degradation
fast =
- seconds/minutes
- in response to hormones e.g. adrenaline or metabolites
- location
- allosteric control
- covalent modification
What does turnover mean?
- the number of substrates that can be converted into product from binding with enzymes per second
- an enzyme with a high turnover will be effected quicker from regulation
what are covalent modifications?
Includes
- hydrolysis of the peptide
- addition of a molecule to a side chain or to the N- or C-terminus of the protein.
- phosphorylation
- very quick effects
What is the allosteric site?
a site on the enzyme other than the active site
What is an isozyme?
Enzymes that catalyse the same reaction but have different chemical composition and different physical properties
describe how the isozymes PKF-2/FBPase-2 works
- it is a bifunctional enzyme (different versions of the same enzyme that have different effects in different parts of the body, like lipoprotein lipase)
- one catalyses forward reaction and one catalyses backwards reaction
- different isoforms in the heart, liver, and lung, and each organ enzyme is activated by different things
reaction:
fructose <–> fructose 2-6-bisphosphate
- PFK-2 = phosphofructokinase-2 = forwards
- FBPase-2 = fructose bisphophatase-2 = backwards
what are the 5 types of enzyme inhibition?
- irreversible
- reversible
- competitive
- uncompetitive
- non-competitive
What is irreversible inhibition?
- Something covalently bonds to active site.
- Cannot be removed.
- lowers the concentration of active enzyme, but the affinity is the same ( as only the few modified enzymes stop binding to the substrate, the rest of the enzymes are unaffected and affinity is the same)
- so Vmax decreases but Km is unchanged
A few bind non-covalently.
give an example of an irreversible inhibitor
penicillin,
aspirin:
- irreversibly binds inhibiting cyclooxgenase 1 and 2 which converts arachidonic acid into prostaglandins are thromboxanes ( used in clotting and inflammation)
- so it is anti-inflammatory, anti-platelet and anti-clotting so it is used to lower risk of heart attacks and as a pain killer with effects of blood thinning
what is a reversible inhibitor?
- a substance that binds to an enzyme to inhibit it, but can be released
- so temporary decrease in Vmax when bound, but Km is not effected
give an example of a reversible inhibitor
protease inhibitors
What is competitive inhibition?
- Compete for active site or bind to allosteric site and alter active site
- Can be overcome by increasing substrate concentration.
- increases the Km (more substrate required to achieve the same rate), but doesn’t change Vmax as the activity of enzyme isn’t affected
- Often resembles the substrate/ similar structure
give an example of a competitive inhibitor
- statins = used to lower cholesterol levels in blood
- class of HMG-CoA reductase which is the rate-limiting enzyme in cholesterol bio-synthesis
- statins inhibit HMG-CoA and cause accumulation of mevalonate (substrate) which signals to decrease cholesterol metabolism and uptake it from the blood
what is an uncompetitive inhibitor?
- binds only to the enzyme-substrate complex (cannot bind to enzyme alone) -think of protective UNcle = only around when get a bf (a substrate)
- moves the E + S = ES = EP equilibrium towards ES which increases the affinity of the enzyme for the ones that aren’t inhibited but decreases the activity overall as some are inhibited
- so the Km is decreased and the Vmax is decreased
give an example of an uncompetitive inhibitor
- lithium used to treat manic depressive psychosis and bipolar disorder
- an uncompetitive inhibitor of inositol monophosphatase which is used in phosphoinositide signalling which affects brain activity, such as reducing dopamine and glutamate but increases GABA and serotonin
- a small therapeutic range so lithium levels need to be regularly measured to avoid toxicity
What is non-competitive inhibition?
- Doesn’t attach to the active site, attaches to the allosteric site, and changes the shape of the enzyme /active site so the substrate doesn’t fit as well.
- can bind to the bound or unbound enzyme, but doesn’t resemble the substrate
- Lowers Vmax, Km is unchanged ( as fewer enzymes can bind so activity decreases and the active site is altered to increasing the substrate will not make a difference)
- binds to both E and ES so E + S = ES equilibrium is unchanged so Km is unchanges
give an example of non-competitive inhibitors
- protein kinse inhibitors
- heavy metal ions
what are protein kinase inhibitors?
- protein kinases are an important group of enzymes which modify proteins by phosphorylating them which usually activates them
- protein kinase inhibitors are usually ATP-competitive, but ATP conc in cells is very high so the competitive inhibitors need a very high affinity to have an effect and have low specificity
- so we need to find a non-competitive inhibitor which is more specific and is not affected by ATP
why are enzymes used for diagnosis?
- because they are highly specific, they can be used to test for certain substances to verify presence or measure conc
describe 5 ways enzymes are used in diagnosis
- measurement of metabolites
- glucose peroxidase enzyme (glucose conc)
- measurement of enzymes
- myocardial infarction (CK-MB detection)
- liver disease ( measure enzyme conc associated with fatty liver disease)
describe using enzymes to measure metabolites
- sample should be diluted so substrate conc < Km and enzyme conc should be in excess
- this is so the enzyme is not saturated
- so rate of reaction is dependent on conc of metabolite/substrate you want to measure
describe using enzymes for glucose peroxidase assay
- alpha glucose reacts with mutarotase to form beta glucose which reacts with glucose oxidase to form hydrogen peroxide
- peroxidase uses hydrogen peroxide to oxidise a colourless compound and make it coloured
- so the absorption of this colour = glucose conc in sample
describe the measurement of enzymes method
- enzyme should be saturated, so high substrate conc
- Vmax is recorded
1 unit of enzyme activity = 1 micromole of substrate converted per minute
describe how enzymes are used to detect myocardial infarction
- injury of heart tissue during myocardial infarction causes cellular proteins to be leaked into plasma
- CK = creatine kinase which is found in lots of tissues but only CK-MB is found in the heart but is normally trapped in cells
- so CK-MB presence in plasma can confirm a recent/current myocardial infarction
