Nitric Oxide Fluorometric Assay Kit

Catalog #K252-200; 200 assays; Store kit at –20^oC)

I. Introduction:

Nitric oxide (NO) plays an important role in neurotransmission, vascular regulation, immune response and apoptosis. Since NO is rapidly converted to nitrite (NO₂^-) and nitrate (NO₃^-), the total concentration of nitrite and nitrate is used as a quantitative measure of NO production. BioVision’s Nitric Oxide Fluorometric Assay Kit provides an accurate and convenient measurement of total nitrate/nitrite concentration in a simple two-step process. In the first step nitrate is converted to nitrite by nitrate reductase. In the second step, nitrite reacts with the fluorescent probe DAN (2, 3 diaminonaphthalene). NaOH enhances the fluorescent yield. The fluorescent intensity is proportional to the total nitric oxide production. The kit has been tested with culture media, plasma, and tissue homogenates.

II. Kit Contents:

III. Reconstitution of Reagents:

1. Assay Buffer: The assay buffer is ready to use as supplied. Store at 4^oC.

1. 
   

   Enzyme Cofactors: Reconstitute with 1.2 ml of Assay Buffer. Aliquot desired amount and store at -20^oC. Keep on ice during use. Freeze/thaw should be limited to 1 time.

   
   


2. 
   

   Enhancer: Reconstitute with 1.2 ml of Assay buffer. Keep on ice during use. Store at -20°C.

   
   


3. 
   

   Nitrate Reductase: Reconstitute with 1.2 ml of Assay Buffer. Aliquot desired amount and store at –20^oC. Keep on ice during use. Freeze/thaw should be limited to 1 time.

   
   


4. 
   

   Nitrate/Nitrite Standards: Reconstitute with 1.0 ml of Assay Buffer, vortex to generate 10 mM standard each. Store at 4^oC when not in use (do not freeze!). The reconstituted standards are stable for 4 months when stored at 4^oC.

   
   


5. 
   

   Fluorometric DAN Probe and NaOH: Ready to use. Store at 4^oC.

   
   

0. 
   

   Measurement of Nitrate + Nitrite:

   
   

1. 
   

   Prepare standards: Add 5 µl of the reconstituted 10 mM nitrate/nitrite standards to 995 l assay buffer, vortex to generate 50 µM working Standard Solution. Add 0, 4, 8, 12, 16, 20 µl of the working Standard to 6 consecutive wells to generate 0, 200, 400, 600, 800, 1000 pmol/well standard. Bring the volume to 75 µl with Assay Buffer.

   
   

Note: DAN Probe reacts with nitrite, not nitrate. For routine total nitrite/nitrate assay, you may prepare a nitrate standard curve only. However, if you need to measure nitrite and nitrate concentrations separately, you may prepare a nitrite standard curve in the absence of Nitrate Reductase in the standard curve and assay samples. Nitrate = Total – Nitrite.

2. 
   

   Prepare Samples: Samples containing high protein concentration may need to be filtered through a 10Kd MW cut-off filter (BioVision Cat # 10KC-20) prior to assay. Add 0-75 µl of sample to the wells and adjust the volume to 75 µl with Assay Buffer.

   
   

Notes: Typical urine nitrite and nitrate levels are in the 0.2-2mM and 1-20µM range respectively. Typical normal serum levels are 0-20µM and 0-2µM respectively with various disease states elevating these levels significantly. Plasma samples or tissue homogenates should be assayed with no more than 10 µl of undiluted sample. Phenol red and serum in cell culture media may decrease the reading, and thus tandard curve should be made in the same media.

3. 
   

   Add 5 µl of the Enzyme Cofactor mixture to all wells.

   
   


4. 
   

   Add 5 µl of the Nitrate Reductase to nitrate assay wells (unknowns and standards), add 5 µl of buffer in place of Nitrate Reductase (unknowns and standards) when you determine nitrite separately.

   
   


5. 
   

   Cover the plate with the plate cover and incubate at room temperature for 1-4 hrs. 1 hour = ~90% conversion of Nitrate to Nitrite, 2 hours = ~ 95% conversion, 4 hours = ~99% conversion.

   
   


6. 
   

   Add 5µl of Enhancer to each well. Incubate 30 minutes to quench interfering compounds.

   
   


7. 
   

   Add 5 µl of DAN Reagent to each well. Incubate for 10 minutes at room temperature.

   
   


8. 
   

   Add 5 µl of NaOH to each well. Incubate for 10 minutes at room temperature.

   
   


9. 
   

   Read the plate in a fluorometer using Ex. = 360 nm and Em. = 450 nm.

   
   

V. Calculations

1. 
   

   Plot standard curve: Plot fluorescence vs. picomoles nitrate.

   
   


2. 
   

   Determine sample nitrate and nitrite concentrations:

   
   

C = [nitrate + nitrite](µM) =(/ )

OR

C = Sa/Sv, where Sa is the amount of samples as read from standard curve (in pmole), and Sv is the volume of sample added to the well (in l), multiplied by the dilution* factor.

*Dilution is the sample dilution done prior to addition of the sample to the well.