Glycomacropeptide (GMP) is a glycosylated peptide formed during renneting as a fragment of sweet whey.
Acid whey from yogurt or curdling cheese without the use of rennet does not contain GMP.
[1] This makes them the third largest fraction of whey protein isolate, after alpha-lactalbumin and beta-lactoglobulin.
GMP is formed when the casein micelle that encapsulates milk protein is cleaved by the enzyme chymosin.
Additionally, GMP is the only easily attainable source of dietary peptides that does not contain any aromatic amino acids.