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NBME 24 Answers

nbme24/Block 3/Question#18 (20.4 difficulty score)
A 55-year-old man with alcoholism is brought ...
Competitive inhibitor🔍

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 +4  upvote downvote
submitted by mcl(517),
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oolll so dnetasi of ngsiu zimfpeloeo yhet stju oagnn etg ihm ealr kurdn

johnson  yep - supposedly, ethanol is used when a hospital/facility doesn't have fomepizole. +5  
usmlecrasherss  Drink vodka man , either way you're dying +  
drschmoctor  Or if you really wanna get drunk and have a warm place to sleep, drink a bunch of methanol in the waiting room of the ED, then let them pump you full of ethanol and keep you safe. +1  

 +3  upvote downvote
submitted by m-ice(272),
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pemotteiiCv nbiiihtors eescrnai eth Km of the .attbsrseu hTe mK nesreretps who siyeal a tbastuesr anc idnb het eativc sti,e thwi a wlore Km gsrnpeeirent yeas idgbinn, adn a hhegri mK ngeiman roem fuitfcdl.i fI yuo dad a cvpitoemtei rit,iionhb lkei eotnlah ni ihst as,ce ti smkea it more itiflfcdu orf the hnomalet ot ibnd eht cvatei i,est ueasebc it smtu peoectm ihtw the el.nhaot

deathbystep1  but how is ethanol a "inhibitor" of alcohol dehydrogenase? isnt the concept that both ethanol and methanol compete for the same binding site of alcohol dehydrogenase and hence ethanol displaces methanol preventing its metabolism? if ethanol were to be a inhibitor it would have to shut off the enzyme, which is does not. +  
krewfoo99  @deathbystep1 Competitive inhibitor simply means increasing concentration of a particular substrate will allow more binding of the substrate to the enzyme. Thus the substrate with the higher concentration will competitive inhibit the other substrate by binding to the enzyme. It dosent necessarily shut off the enzyme +2  

 +0  upvote downvote
submitted by madojo(122),

The Km is inversely related to the affinity of the enzyme for its substrate so in this case we want to increase Km so that the affinity of hepatic alcohol dehydrogenase decreases for methanol and the ethanol can then act as a competitive inhibitor by overcoming the concentration of methanol thus preventing toxicity.