Introduction to chemistry of proteins

Stereochemistry (Optical activity)

Stereochemistry mainly emphasizes the configuration of amino acids at the α carbon atom, having either D or L- isomers.

      COOH                                         COOH

       |                                                     |

 H - C – NH₂                             H₂N – C – H

       |                                                     |

      R                                                    R

D (+) amino acid                      L (-) amino acid

D and L- forms of Amino acids

Out of the 20 amino acids, proline is not an α amino acid rather an α - imino acid. Except for glycine, all amino acids contain at least one asymmetric carbon atom (the α - carbon atom).