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Endorphins are natural peptide hormones in number of neurochemical processes. fa

ID: 224300 • Letter: E

Question

Endorphins are natural peptide hormones in number of neurochemical processes. famously, they act as neurotransmitters that the opioid receptors in our brains (the same receptors bound by morphine and heroin), stimulating feelings of well-being and providing pain relief. One of the most common endorphins is Leu-Enkephalin, shown above. What is the amino acid sequence of Leu-Enkephalin? Estimate its pl. Leu-enkephalin relies on a membrane-bound protein receptor, called an opioid receptor, interact with nerve cells. What amino acids might you expect to find located in the active binding site of the opioid receptor for Leu-Enkephalin? Why?

Explanation / Answer

(7) the amino acid sequence Tyr-Gly-Gly-Phe-Leu

None of the amino acids in the peptide have ionizable side chains. Therefore the pI (isoelectric pH ) will be the average of pKa of amino group and pKa of carboxyl groups

=(9.1+2.3)/2 =5.7