• Purity

  >95%, by SDS-PAGE visualized with Silver Staining and quantitative densitometry by Coomassie? Blue Staining.

• Endotoxin Level

  <1.0 EU per 1 μg of the protein by the LAL method.  

• Activity

  Measured by its ability to transfer phosphate from ATP to GMP. The specific activity is >7,500 pmol/min/μg, as measured under the described conditions.

• Source

  E. coli-derived Ser2-Ala197, with an N-terminal Met and 6-His tag

• Accession #

• N-terminal Sequence    
  Analysis

  Met

• Predicted Molecular Mass

  23 kDa

• SDS-PAGE

  24 kDa, reducing conditions

Assay Procedure

Materials

• Universal Kinase Activity Kit (Catalog # )

• 10X Assay Buffer (supplied in kit):  250 mM HEPES, 1.5 M NaCl, 100 mM MgCl₂, 100 mM CaCl₂, pH 7.0

• Recombinant Human Guanylate Kinase (rhGUK-1) (Catalog # 9267-GU)

• Guanosine 5'-monophosphate (GMP) (Sigma, Catalog # G8377), 10 mM stock in deionized water

• 96-well Clear Plate (Catalog # )

• Plate Reader (Model: SpectraMax Plus by Molecular Devices) or equivalent

1. Prepare 1X Assay Buffer by diluting 10X stock 10 fold with deionized water.

2. Dilute 1 mM Phosphate Standard by adding 40 μL of the 1 mM Phosphate Standard to 360 μL of 1X Assay Buffer for a 100 μM stock.  This is the first point of the standard curve.

3. Continue standard curve by performing six one-half serial dilutions of the 100 μM Phosphate stock in 1X Assay Buffer.  The standard curve has a range of 0.078 to 5 nmoles per well.

4. Prepare a reaction mixture containing 0.2 mM ATP (supplied in kit) and 0.2 mM GMP in 1X Assay Buffer.

5. Dilute rhGUK-1 to 0.0667 μg/mL 1X Assay Buffer.

6. Load 50 μL of each dilution of the standard curve into a plate.  Include a curve blank containing 50 μL of 1X Assay Buffer.

7. Load 15 μL of the 0.0667 μg/mL rhGUK-1 into empty wells of the same plate as the curve. Include a Control containing 15 μL of 1X Assay Buffer.

8. Add 25 μL of reaction mixture to all wells, excluding standard curve.

9. Seal plate and incubate at room temperature for 30 minutes.

10. Dilute Coupling Phosphatase 4 (supplied in kit) to 10 μg/mL 1X Assay Buffer.

11. Add 10 μL of 10 μg/mL Coupling Phosphatase 4 to wells containing enzyme and control, excluding the standard curve.

12. Seal plate and incubate at room temperature for 5 minutes.

13. Add 30 μL of the Malachite Green Reagent A to all wells.  Mix briefly.

14. Add 100 μL of deionized water to all wells. Mix briefly.

15. Add 30 μL of the Malachite Green Reagent B to all wells.  Mix and incubate for 20 minutes at room temperature.

16. Read plate at 620 nm (absorbance) in endpoint mode.

17. Calculate specific activity:

*Derived from the phosphate standard curve using linear or 4-parameter fitting and adjusted for Control.
**Incubation time is 35 minutes according to the above protocol.
***Both ADP and GDP can be digested by Coupling Phosphatase 4 and release one unit of phosphate.

Per Reaction:

• rhGUK-1: 0.001 μg

• Coupling Phosphatase 4: 0.1 μg

• ATP: 0.1 mM

• GMP: 0.1 mM

Background: Guanylate Kinase

GUK1, also known as GMP kinase, belongs to the guanylate kinase family. This protein exists as a monomer and catalyzes the ATP-dependent conversion of GMP to GDP, thereby playing an essential role in the recycling of GMP (1). Via its catalytic activity, GUK1 participates in regulating the supply of guanine nucleotides including cGMP to signal transduction pathways (2). GUK1 is widely expressed. Overexpression of GUK1 is associated in pituitary adenomas (3). The enzymatic activity of the recombinant human GUK1 is measured using a phosphatase-coupled method (4).

• References:

1. Brady, W.A. et al. (1996) J. Bio.Chem. 271:16734.

2. Fitzgibbon, J. et al. (1996) FEBS Letters 385:185.

3. Da Rocha, A.A. et al. (2006) Pituitary 9:83.

4. Wu, Z.L. (2011) PLoS ONE 6:e23172.

• Entrez Gene IDs:

  2987 (Human); 14923 (Mouse); 303179 (Rat)

• Alternate Names:

  ATP:GMP Phosphotransferase; Deoxyguanylate Kinase; EC 2.7.4.8; FLJ42686; FLJ43710; GMK; GMP Kinase; Guanosine monophosphate Kinase; guanylate kinase 1; Guanylate Kinase; GUK1