By Pure Encapsulations. Methionine is an essential amino acid that contains sulfur, which is an important component of cartilage building blocks such as proteoglycans and glycosaminoglycans. Methionine is incorporated into tissue proteins and enzymes and is a component of active peptides, including methionine enkephalin and various endorphins. One of the main roles of methionine is as a methyl donor, contributing to numerous physiological pathways in the body including formation of myelin components. In one such pathway, methionine converts to s-adenosylmethionine.