Proline


 * Proline** (abbreviated as **Pro** or **P**) is an α-[|amino acid], one of the twenty [|DNA]-encoded amino acids. Its [|codons] are CCU, CCC, CCA, and CCG. It is not an [|essential amino acid], which means that the human body can synthesize it. It is unique among the 20 protein-forming amino acids in that the α-amino group is [|secondary]. The more common L form has //S// stereochemistry.

Richard Willstatter synthesized this by the reaction of salt in 1900.

Proline and its derivatives are often used as asymmetric catalysts in organic reactions. The [|CBS reduction] and proline catalysed [|aldol condensation] are prominent examples. L -Proline is an [|osmoprotectant] and therefore is used in many pharmaceutical, biotechnological applications. In brewing, proteins rich in proline combine with polyphenols to produce haze (turbidity).

Isomerization
Peptide bonds to proline are able to populate both the "cis" and //"trans"// isomers. Most peptide bonds overwhelmingly adopt the // trans // isomer because the amide hydrogen ( // trans // isomer) offers less steric repulsion to the preceding atom than does the following  atom ( // cis // isomer). By contrast, the // cis // and // trans // isomers of the X-Pro peptide bond (where X represents any amino acid) both experience steric clashes with the neighboring substitution and are nearly equal energetically. So the peptide bonds in the // cis // isomer under unstrained conditions ranges from 10-40%; the fraction depends slightly on the preceding amino acid, with aromatic residues favoring the // cis // isomer slightly.

Specialities
Proline is one of the two amino acids that do not follow along with the typical Ramachandran, along with glycine. Due to the ring formation connected to the Beta-carbon, the ψ and φ angles about the peptide bond have less allowable degrees of rotation. As a result it is often found in "turns" of proteins as its free entropy (ΔS) is not as comparatively large to other amino acids and thus in a folded form vs. unfolded form, the change in entropy is less. Furthermore, proline is rarely found in α and β structures as it would reduce the stability of such structures, because its side chain α-N can only form one hydrogen bond.

Uses:
Proline and its derivatives are often used as asymmetric catalysts in organic reactions. The CBS reduction and proline catalysed aldol condensation are prominent examples. L-Proline is an osmoprotectant and therefore is used in many pharmaceutical, biotechnological applications. In brewing, proteins rich in proline combine with polyphenols to produce haze (turbidity)

History:
Richard Willstätter synthesized proline by the reaction of sodium salt of diethyl malonate with 1,3-Dibromopropane in 1900. In 1901, Hermann Emil Fischer isolated proline from casein and the decomposition products of γ-phthalimido-propylmalonic ester.[