Amino Acids: Difference between revisions
Eric Martz (talk | contribs) |
Eric Martz (talk | contribs) |
||
| Line 135: | Line 135: | ||
The asymmetric α-carbon in 19 of the standard amino acids (all except glycine) is a chiral center<ref name='chirality' />. Thus, each amino acid can exist in either of two optical isomers or enantiomers (mirror images), designated the L-form and D-form. Nearly all naturally-occuring amino acids are L-amino acids, so named because they are analogous to the L-form of glyceraldehyde<ref name='chirality'>See [http://en.wikipedia.org/wiki/Chirality_(chemistry) Chirality in Wikipedia]].</ref>. (Not all L-amino acids are levorotatory; some rotate polarized light clockwise<ref name='chirality' />). | The asymmetric α-carbon in 19 of the standard amino acids (all except glycine) is a chiral center<ref name='chirality' />. Thus, each amino acid can exist in either of two optical isomers or enantiomers (mirror images), designated the L-form and D-form. Nearly all naturally-occuring amino acids are L-amino acids, so named because they are analogous to the L-form of glyceraldehyde<ref name='chirality'>See [http://en.wikipedia.org/wiki/Chirality_(chemistry) Chirality in Wikipedia]].</ref>. (Not all L-amino acids are levorotatory; some rotate polarized light clockwise<ref name='chirality' />). | ||
Although D-amino acids are rare in nature, they do occur (see [http://en.wikipedia.org/wiki/Chirality_(chemistry)#D-Amino_Acid_Natural_Abundance natural abundance in Wikipedia]). D-alanine (DAL) occurs in over 100 entries in the [[PDB]], D-leucine (DLE), D-phenylalanine (DPN), D-serine (DSN), and D-valine (DVA) each occur in over 50. Some of these entries are chemically synthesized, not naturally occuring. Gramicidin is a naturally occuring antibiotic containing several D-amino acids, e.g. [[1nrm]]. [[4glu]] is the 102 amino acid chain of VEGF-A synthesized entirely from D-amino acids. | More than 700 entries in the [[PDB]] contain one or more D amino acids. Although D-amino acids are rare in nature, they do occur (see [http://en.wikipedia.org/wiki/Chirality_(chemistry)#D-Amino_Acid_Natural_Abundance natural abundance in Wikipedia]). D-alanine (DAL) occurs in over 100 entries in the [[PDB]], D-leucine (DLE), D-phenylalanine (DPN), D-serine (DSN), and D-valine (DVA) each occur in over 50. Some of these entries are chemically synthesized, not naturally occuring. Gramicidin is a naturally occuring antibiotic containing several D-amino acids, e.g. [[1nrm]]. [[4glu]] is the 102 amino acid chain of VEGF-A synthesized entirely from D-amino acids. | ||
==Unusual Amino Acids== | ==Unusual Amino Acids== | ||