Along with HPLC methods for measuring brain monoamine neurotransmitters or circulating levels of the antioxidant glutathione, I received a very insightful write up on amino acids and the role they play in the human body from scientists in our Chelmsford Center of Excellence, based in Massachusetts, United States.
Here is the write up in its entirety!
Did you know that each of the naturally occurring amino acid used by our bodies to make proteins occur in two forms, commonly called L- (left) and D- (right) isomers?
These isomers are said to be chiral, that is they exist as non superimposable mirror image pairs. Think of your left and right hands – they are mirror images of each other – no matter how you orient them, it is impossible for all the major features of both hands to coincide. Perhaps this difference in symmetry becomes most obvious when you try to put a left-handed glove on your right hand. But why does symmetry matter? Well, it turns out that different isomers of the same compound, even though they have the same chemical formula, can show major differences in function and activity. For example, we need sugars in our diet, but if we were to eat the L-form of these sugars we would starve, as our body can only metabolize the D-form. These differences are taken advantage of by some artificial sweeteners. Tagatose (or Naturlose), are the mirror-image of milk-sugar and taste sweet, but because we cannot absorb them, they have zero calories. Amino acids occur as L- and D- forms, too. The isomers of the amino acid phenylalanine have different tastes, with the D-form tasting sweet whereas the L-form is bitter.
For many years, the thinking amongst scientists was that only L-amino acids occurred in higher organisms such as mammals, with D-amino acids being more common in simpler organisms like bacteria. D-amino acids were not even thought to exist in higher organisms at all. However, recent studies have shown that some D-amino acids are not only present in high concentrations in animals and humans but they actually fulfill specific biological functions. Two amino acids, serine and aspartic acid are receiving special attention.
L-Aspartic acid is a component of proteins but also takes part in several important biochemical pathways. It is also an excitatory chemical messenger that stimulates brain activity. The possible biological importance of D-Aspartic acid is less certain but it appears to be important with an organism’s development and proper glandular function. Interestingly, it is currently being marketed as a testosterone-boosting supplement to body builders, but some recent studies are questioning this claim (link to study).
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L-Serine, a proteinogenetic amino acid, is also used by the body to make proteins but, in addition, it is key to the functioning of some enzymes and plays an important role in many biochemical pathways. D-Serine, (link to research study), the second D-amino acid to be found in brain, is essential for normal brain activity (link to research study) and may play a crucial part in diseases such as schizophrenia, ischemia, epilepsy, and neurodegenerative disorders (link to research study).
In order to evaluate their biological roles in health and disease, it is necessary to accurately measure D-amino acids tissue levels. This might aid in disease diagnostics and treatment. Analysis is particularly challenging as it is difficult to separate and accurately measure each amino acid’s L- and D- isomers. To help tackle this problem, we developed a simple HPLC-based method described in Application Note 1071, Fast UHPLC Method for the Simultaneous Determination of Free D-Aspartic Acid and D-Serine in Brain Tissue Extracts, (downloadable PDF), using automated derivatization and fluorescence detection to measure different amino acid isomers in brain samples. The method is simple, straightforward, selective and highly sensitive. It features the use of our rapid-separation HPLC systems (Thermo Scientific Dionex UltiMate 3000 RSLC system) equipped with one of our fluorescence detectors (Thermo Scientific Dionex UltiMate FLD-3400RS Fluorescence Detector with Dual-PMT) and one of our ultrapure, high-resolution HPLC columns (Thermo Scientific Hypersil GOLD HPLC column).
By the way, if you are looking to determine brain monoamine neurotransmitters, or circulating levels of the antioxidant glutathione do check out Application Note 1060, Comprehensive Neurochemical Profiling of Brain Tissue Samples (downloadable PDF) and Poster Note, Simple, Rapid Analysis of Aminothiols with Boron-Doped Diamond Electrochemical Detection (downloadable PDF). Both approaches take advantage of our highly sensitive and selective electrochemical detector and analytical cells.
If you have questions on this method, or the column and instrument used, do enter them in the Comments box below; our experts look forward to hearing from you.