Proline

Between 1899 and 1906, Hermann Emil Fischer discovered the amino acid Proline. Proline, abbreviated as Pro or P, is one of the twenty DNA-encoded amino acids. The systematic name for Proline is Pyrrolidine-2-carboxylic acid. It is not considered an essential amino acid; therefore the human body can synthesize it. Proline is the only cyclic amino acid and is biosynthetically derived from the amino acid,  L-glutamate and its immediate precursor is the imino acid (S)-1-pyrroline-5-carboxylate (P5C).¹ An imino acid is any molecule that contains both imino (>C=NH) and carboxyl (-C(=O)-OH) functional groups.² Proline is used a systemmatic catalyst in organic reactions. L-Proline is an osmoprotectant and therefore is used in many pharmaceutical, biotechnological applications.¹ Proline is thermophilic and can withstand an environment with extreme osmotic stress, thus why proline is widely used in pharmaceuticals. In studying Immunology, proline plays a significant role. Proline-rich polypeptides (PRP), such as the proline-rich polypeptide in ovine colostrum has an effect on skin permeability and immune response.³

When researching this amino acid, I found it interesting that, “proline is the only amino acid that does not form a blue/purple colour when developed by spraying with ninhydrin for uses in chromatography. Proline, instead, produces an orange/yellow colour.”¹ In our Organic I and II labortories, we use chromatography. The pK value for the amide is 11.0 and the pK value for the carboxyl group is 2.0.⁴

1. http://en.wikipedia.org/wiki/Proline

2. http://en.wikipedia.org/wiki/Osmoprotectant

3.  http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1457668/
4. http://www.biology.arizona.edu/biochemistry/problem_sets/aa/proline.html

Electrophilic Aromatic Substitution Journal

In Biotech Business Week, September 3, 2007, BIOMEDICINE; Report summarizes biomedicine study findings from Osaka City University, Department of Chemistry was published. The experiment's goal is to determine the monoxygenase activity of three copper proteins and undergo ortho-hydroxylation of phenols and later electrophilic aromatic substitution to give the final product. During this experiment, the third copper protein tested undergoes electrophilic aromatic substitution. Lithium phenolates and peroxo dicopper(II) will react by electrophilic aromatic substitution to give an oxygenated product called catechols. The researchers  determined that the monoxygenase activity is similar to that of tyrosinase because they both undergo a simple enzymatic reaction that is the same mechanism as electrophilic aromatic substition. In the conclusion, the author states, "In this case as well, the ortho-hydroxylation of phenols to catechols has been demonstrated to involve the same ionic mechanism." The ionic mechanism being electrophilic aromatic substitution.

Jesslyn

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