meg
Forum Guru
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Posts: 806
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During the isolation of Met-enkephalin(Tyr-Gly-Gly-Phe-Met) from post mortem human brain tissue, researchers find that the peptide is rapidly degraded by peptidases in 1 min at 37 degrees C. Detailed analysis of the peptide cleavage pattern of Met-enkephalin is investigated with two candidate enzymes. Using the drug bestatin, the investigators found no detectable Tyr-Gly-Gly-Phe-Met but found significant concentrations of Tyr-Gly-Gly. Using thiorphan, there was no detectable Tyr-Gly-Gly-Phe-Met , but there was high concentration of Tyr. Which of the following is the best conclusion about Met-enkephalin metabolism that can be drawn from this data?
A: Bestatin inhibits an aminopeptidase, and thiorphan inhibits an endopeptidase in the degradative pathway
B: Bestatin inhibits an carboxypeptidase
C:Bestatin inhibits an endopeptidase in the degradative pathway
D: Thiorphan inhibits an aminopeptidase and bestatin inhibits an endopeptidase in the degradative pathway
E: Thiorphan inhibits an aminopeptidase in the degradative pathway.
Please explain your answer.
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| MIG
Forum Junior
Topics: 6
Posts: 63
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I think answer is B
If i am right , my explanation will be like that:
Met enkephalin have structure = Tyr-Gly-Gly-Phe-Met
1.Bestatin cleave that peptide on a Gly (specificaly cut on the carboxil COOH side of glycin) and give us fragment Tyr-Gly-Gly
2.Thiorphan cleave on a Tyr ( also on a carboxyl end), give us only Tyr fragments
That is why , by my thinking Bestatin inhibits an carboxypeptidase(b).
please tell me if i am right or wrong , and explain to me too. almost the same problem was on exam
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| Yulia
Forum Elite
Topics: 19
Posts: 240
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Hello MIG,
Tyr-Gly-Gly-Phe-Met is a peptide, tyr being an amino-end and met - carboxyl-end.
bestatine gives us a fragment Tyr-Gly-Gly meaning that endopeptidase is working in this case. and aminopeptidase is not, because there's no tyr detectable.
with thiorphan we have high concentration of tyr, so we can assume aminopeptidase is active. and endopeptidase is not, otherwise we would have Tyr-Gly-Gly fragment as well.
So, we can conclude that bestatine inhibits aminopeptidase, and thiorphan inhibits endopeptidase. A is correct.
option B is wrong, because carboxypeptidase is not used here, so we can't tell it's inhibited by either of 2 drugs.
C is wrong, because we said endopeptidase was active when they used bestatine (Tyr-Gly-Gly fragment present)
D and E are wrong as well. explanation above.
Hope this helps. Good luck.
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| docchenah
Forum Newbie
Topics: 4
Posts: 27
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I am preparing for my test for friday and came across this question in qbank and it was driving me up the wall. I am so grateful I found the explanation to this. Thank you so much 
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| sturge_weber
Forum Guru
Topics: 77
Posts: 1,042
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yes awesome explanation
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