As a practical excercise in teaching 16-year-olds the mechanics of protein synthesis I use a cut and paste and move components around task copied from someones copy of a copy of an unknown book.
The intro text on the excercise sheet says “Endorphin … consist of just five amino acids in this order: Tyr-Gly-Gly-Phe-Met”
After using it for a few years I figured it’d be fun to show the structure of the actual molecule, and I was wondering how over-simplified the explanation was since it didn’t match my growing understanding of protein synthesis and I discover that beta and alfa endorphin may start with Tyr-Gly-Gly-Phe-Met but are actually much longer chains and also the result (as I suspected) of an even larger precursor being synthesised and then chopped into pieces.
So I’m wondering, is the sentence “Endorphin … consist of just five amino acids in this order: Tyr-Gly-Gly-Phe-Met” just a complete lie from the creator of the exercise, or could a biochemist find a way to justify it as a lie-to-children simplification?
How can one give one formula for EVERY endorphin.. there are lots of endorphins.
That formulai s for Met-enkephalin
Met-enkephalin, sometimes referred to as opioid growth factor is a naturally occurring, endogenous opioid peptide that has opioid effects of a relatively short duration. It is one of the two forms of enkephalin, the other being leu-enkephalin. The enkephalins are considered to be the primary endogenous ligands of the δ-opioid receptor, due to their high potency and selectivity for the site over the other endogenous opioids.
So my Norwegian online medical dictionary has enkephalins as a subgroup of endorphins, while Wikipedia has endorphins and enkephalins as separate subgroups of opioid peptides. Does this reflect changes in how the terms are used, or differences between countries?
Both human pro-enkephalin A and pro-enkephalin B are produced as large proteins (>250 amino acids). They start with a 20 AA pre-sequences required for secretion and get cleaved by protease to each yield several different biologially active peptides.
Endorphin is a functional description for endogenous peptides that bind to the opoid receptors. Met-enkephalin and Leu-enkephalin are 5-amino acid peptide fragments of the two enkephalin precursor protein that happen to show endorphin activity.