D-amino acids are not as widespread as their enantiomeric counterparts in proteins, but they can be found in organisms ranging from bacteria (cell walls and antibiotics) to mammals (central nervous systems). Aberrant levels of D-serine are associated with diseases caused by abnormal NMDA receptor activity. Increased levels of D-serine in the cerebrospinal fluid (CSF) have been detected in patients with Alzheimer’s disease compared to normal controls. Decreased D-serine levels (which lowers NMDA receptor signaling) is associated with schizophrenia-like symptoms.

D-Amino Acid Assay Kit provides a simple, reproducible, and sensitive tool for measuring D-Amino Acid (except for D-Glutamate, D-Aspartate and Glycine) concentration in plasma, serum, cell lysates, saliva, urine, and other biological liquid samples. This assay employs a coupled enzymatic reaction system that combines multiple steps. D-Amino Acid is oxidized by D-Amino Acid oxidase, resulting in a colorimetric (570 nm) / fluorometric (Ex/Em = 535/585 nm) product. The absorbance / fluorescence measured is directly proportional to the concentration of D-Amino Acid present in the sample.

• Microplate reader capable of measuring OD 570 nm or Ex/Em = 535/585 nm
• 96-well black plate for fluorometric assay
• Precision pipettes to deliver 2 µL to 1 mL volumes
• Tubes to prepare sample dilutions
• Incubator at 37°C
• 5 mL tubes
• Multi-channel pipettes to deliver 20 µL to 200 µL volumes
• MilliQ water or another type of double distilled water (ddH₂O)

1. Add 50 µL of the diluted D-Alanine standards or samples to the 96-well microtiter plate.
2. Add 50 µL Reaction Mix to each standard and one half of the paired sample wells, mix thoroughly.
3. Add 50 µL of Control Mix to other half of the paired sample wells. Carefully shake the plate for a few seconds to mix.
4. Incubate the plate for 30 minutes at 37°C with mixing in the dark.
5. Measure the absorbance at 570 nm or fluorescent intensity at Ex/Em 535/585 nm using a plate reader.