1.9. Inhibitors Flashcards
inhibitors
substances that reduce the enzyme activity, specific for an enzyme
- prevent the S from joining with the active site
- competitive or non-competitive
- reversible or irreversible
competitive inihibition
- inhibitors compete with S for the active site
- specific for the enzyme (active site)
- increase in C(S) reduces their effect (S prevails)
non-competitive inhibition
- inhibitors bind to the allosteric site of an enzyme
- changing the conformation of the E, changing its active site, S cannot attach
- function not impacted by change in C(S)
example of competitive inhibition
enzyme alcohol dehydrogenase oxidizes methanol into formaldehyde and formic acid (poisonous) - treatment is ethanol ingestion - dehydrogenase has greater affinity for ethanol (competitive inhibitor) - body has more time to eliminate methanol
examples of non-competitive inhibitors
saccharides (artificial sweeteners)
fructose-6-phosphate (S), phosphofructokinase (E), xylitol-5-phosphate (I) - doesn’t get metabolized(/digested, just tastes sweet (xylitol used in food for diabetes and sugar-free products)
r/C(S) graph for no inhibitor, CI and NCI
no-inhibitor - sped up reaction, exponential growth, plateau phase
CI - linear growth, ends at the same point as no inhibitor reaction (sped up because C(S) lowers I effect)
NCI - same curve as no-inhibitor but lower finishing point (slowed down by inhibitors, not affected by C(S))
allosteric interaction
- interaction between an E and chemical that binds to its allosteric site
- negative allosteric regulation - NCI
- positive allosteric regulation - activators increase E’s affinity for a S
two types of pathways in metabolic reactions
cyclic and linear (chain)
end product inhibition
- end product acts as an inhibitor for the 1st enzyme along the metabolic process (chain) - excess P inhibits to prevent accumulation
example of end product inhibition
threonine (ess.) and isoleucine (non-ess. a-a), Is binds to allosteric site of E1 and inhibits it - prevents overproduction - reversible, can unbind when more of Is is needed
Why are some heavy metals toxic for the body?
they act as non-competitive inhibitors - they irreversibly bind with an enzyme, changing its conformation and preventing it from functioning (dangerous) - Hg (Hg2+ with SH of cystine - covalent bonds formed between), Pb…
mechanism-based inhibition example - irreversible competitive inhibition
transpeptidase is an enzyme that catalyzes the formation of cross-links between peptide and polysaccharide molecules to form peptidoglycan (which is a major component of bacteria cell wall) - penicillin inhibits transpeptidase (fits instead of peptide chains) - no cell wall, water enters the cell (in hypotonic solution), bacteria bursts/dies
- funghi naturally produce penicillin and fight off bacteria (both saprotrophs - rivals)
