mahendra
Forum Guru
Topics: 173
Posts: 419
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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 minute at 37 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 did
find significant concentrations of Tyr-Gly-Gly. Using thiorphan,
there was no detectable Tyr-Gly-Gly-Phe-Met, but there was a hig
h concentration of Tyr. Which of the following is the best conclusion
about Met-enkephalin metabolism that can be drawn from these data?
A. Bestatin inhibits an aminopeptidase, and thiorphan inhibits an endopeptidase in the degradative pathway
B. Bestatin inhibits a carboxypeptidase in the degradative pathway
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
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| asmi
Forum Hero
Topics: 1043
Posts: 4,609
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A :?:
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the answer is D. Bestatin inhibits endopeptidase - as you are left with an aminoacid sequence which is a fragment of the original met-enkephalin sequence. Only endopeptidase cleaves aminoacids inside the peptide chain.
The other drug is an aminopeptidase inhibitor as it prevents the cleaving of tyrosine at the amino end of the met-enkephalin sequence.
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| Yulia
Forum Elite
Topics: 19
Posts: 240
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this has been answered before 
check this out
http://www.prep4usmle.com/community/topic2439.htm...
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| asmi
Forum Hero
Topics: 1043
Posts: 4,609
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thanks yulia
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