Betaine has three known functions in mammals: It is an organic osmolyte that accumulates in renal medullary cells and some other tissues to balance extracellular hypertonicity. Second, it acts as a chaperone to stabilise protein structure under denaturing conditions. Third, it serves as a methyl donor in the betaine homocysteine methyltransferase (BHMT) reaction, which converts homocysteine to methionine. Betaine is also present as an osmolyte in high concentrations (10s of millimolar) in many marine invertebrates, such as crustaceans and molluscs, and acts as a potent appetitive attractant to generalist carnivores such as the predatory sea-slug Pleurobranchaea californica.
The percentage represents the approximate total number of food products from UPC Food Search's data that contain the ingredient, "Trimethylgycine".