Question

Vitamin K participates in carboxylation of glutamic acid residues of the blood-clotting protein prothrombin. (a) Write a structural formula for \(\gamma\)-carboxyglutamic acid. (b) Account for the fact that the presence of \(\gamma\)-carboxyglutamic acid escaped detection for many years; on routine amino acid analyses, only glutamic acid was detected.

Short answer

Gamma-carboxyglutamic acid was not detected earlier in routine amino acid analyses because of its structural similarity to glutamic acid. Both have closely related structures, with gamma-carboxyglutamic acid containing an additional carboxyl group. The methods used to detect and distinguish different amino acids in routine analyses are often based on their structural differences. Due to this close resemblance, gamma-carboxyglutamic acid was not easily distinguishable from glutamic acid, leading to only glutamic acid being detected.

Step-by-step solution

Structural formula for glutamic acid

Glutamic acid is an amino acid with a molecular formula of C5H9NO4. Its structure can be represented as follows: \[\textrm{H}_{2}\textrm{N}-\textrm{CH}(\textrm{COOH})-\textrm{CH}_{2}-\textrm{CH}_{2}-\textrm{COOH}\]

Structural formula for gamma-carboxyglutamic acid

Gamma-carboxyglutamic acid is a derivative of glutamic acid with an additional carboxyl group. The molecular formula is C6H9NO6, and the structure can be represented as: \[\textrm{H}_{2}\textrm{N}-\textrm{CH}(\textrm{COOH})-\textrm{CH}_{2}-\textrm{CH}(\textrm{COOH})-\textrm{COOH}\]

Explain why gamma-carboxyglutamic acid was not detected during routine amino acid analyses

The reason why gamma-carboxyglutamic acid escaped detection for many years is due to its structural similarity to glutamic acid. In routine amino acid analyses, the methods used to detect and distinguish different amino acids are often based on their structural differences. Since gamma-carboxyglutamic acid is very similar to glutamic acid, with just an additional carboxyl group, it was not easily distinguishable during these analyses. As a result, only glutamic acid was detected.