Proline is one of the cyclic aliphatic amino acids that is a major component of the protein collagen, the connective tissue structure that binds and supports all other tissues. Proline is synthesized from glutamic acid prior to its incorporation into pro-collagen during messenger RNA translation. After the pro-collagen protein is synthesized, it is converted by posttranslational modification into hydroxyproline. On a molar basis proline is incorporated into protein at a rate of 4.2 percent with respect to other amino acids.