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Proline

Proline is a unique amino acid. Instead of having a primary amino group as in other alpha-amino acids, it contains a secondary amine. Proline and hydroxyproline do not possess an aminic group, but an iminic group. Their presence in special polypeptide chain sites allows proteins certain curves which have structural importance. Hydroxyproline is not present in the majority of proteins and is typical of connectival proteins (collagen, elastin); it is contained in collagen as an essential component at a ratio of 10%. L-proline is a useful amino acid which is used as a medicine and in other applications. In the past, L-proline has been produced mainly by isolation from hydrolysates of proteins or gelatin or by organic synthesis. However, the yield of product obtained by these methods is very low, and the procedures involved are complicated. As a result, L-proline is one of the most expensive amino acids.

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