• Purity

  >95%, by SDS-PAGE under reducing conditions and visualized by Colloidal Coomassie? Blue stain at 5 μg per lane

• Endotoxin Level

  <0.10 EU per 1 μg of the protein by the LAL method.  

• Activity

  Measured by its ability to inhibit KLK7 cleavage the fluorogenic peptide substrate, Mca-RPKPVE-Nval-WRK(Dnp)-NH    ₂ (Catalog # ). The IC    ₅₀ is<45 nM, as measured under the described conditions. See Activity Assay Protocol on .  

• Source

  Mouse myeloma cell line, NS0-derived Leu20-Pro411, with a C-terminal 10-His tag

• Accession #

• N-terminal Sequence    
  Analysis

  Leu20

• Predicted Molecular Mass

  47 kDa

• SDS-PAGE

  45-54 kDa, reducing conditions

Assay Procedure

Materials

• Activation Buffer: 50 mM Tris, 10 mM CaCl₂, 150 mM NaCl, 0.05% (w/v) Brij-35, pH 7.5 (TCNB)

• Inhibition Buffer: 25 mM Tris, 150 mM NaCl, pH 7.5

• Assay Buffer: 50 mM Tris, 150 mM NaCl, pH 8.5

• Recombinant Rat Serpin A12 (rrSerpin A12) (Catalog # 8339-PI)

• Recombinant Human Kallikrein 7 (rhKLK7) (Catalog # )

• Bacterial Thermolysin (Catalog # )

• 1,10 Phenanthroline (Sigma, Catalog # 320056), 0.6 M stock in DMSO

• Substrate:  Mca-RPKPVE-Nval-WRK(Dnp)-NH₂ (Catalog # )

• F16 Black Maxisorp Plate (Nunc, Catalog # 475515)

• Fluorescent Plate Reader (Model: Gemini EM by Molecular Devices) or equivalent

1. Combine rhKLK7 with Thermolysin in Activation Buffer for final concentrations of 100 μg/mL and 10 μg/mL, respectively.

2. Incubate rhKLK7 mixture at 37 °C for 2 hours.

3. Add 1,10 Phenanthroline at a final concentration of 10 mM to stop activation reaction.

4. Prepare a curve of rrSerpin A12 (MW = 46987 Da) in Inhibition Buffer.  Make the following serial dilutions: neat, 4000, 2000, 1000, 500, 250, 50, and 5 nM.  (Note: High points may not be achievable due to the stock concentration of some lots).

5. Dilute stopped rhKLK7 to 50 μg/mL in Inhibition Buffer.

6. Combine equal volumes of each point of the rrSerpin A12 curve with 50 μg/mL rhKLK7. Include an enzyme control containing equal volumes of Inhibition Buffer and 50 μg/mL rhKLK7.

7. Incubate curve reaction mixtures at room temperature for 30 minutes.

8. Dilute each point of the curve 12.5 fold using Assay Buffer.

9. Dilute Substrate to 20 μM in Assay Buffer.

10. Load 50 μL each of the diluted curve points to a plate, and start the reactions by adding 50 μL of 20 μM Substrate. Include a Substrate Blank containing 50 μL of Assay Buffer and 50 μL of 20 μM Substrate.

11. Read at excitation and emission wavelengths of 320 nm and 405 nm (top read), respectively, in kinetic mode for 5 minutes.

12. Derive the 50% inhibition concentration (IC₅₀) value for rrSerpin A12 by plotting RFU/min (or specific activity) versus concentration with 4-PL fitting.

13. The specific activity for rhKLK7 at each point may be determined using the following formula:

     *Adjusted for Substrate Blank

     **Derived using calibration standard MCA-Pro-Leu-OH (Bachem, Catalog # M-1975). Per Well:

• rrSerpin A12: (neat/50), 80, 40, 20, 10, 5, 1, and 0.1 nM

• rhKLK7: 0.1 μg

• Substrate: 10 μM

Background: Serpin A12

Serpin A12, also known as Vaspin, is a 45-50 kDa secreted adipokine that contributes to the maintenance of insulin sensitivity (1, 2). It is structurally related to the Serpin family of serine protease inhibitors (3). Mature rat Serpin A12 shares 62% and 88% amino acid sequence identity with human and mouse Serpin A12, respectively (3). It is expressed by adipocytes in visceral and subcutaneous fat, in the gastric glands and epithelium, and in the placenta (3-5). Serpin A12 circulates in a complex with Kallikrein 7, and it prevents the Kallikrein 7 mediated cleavage of Insulin (6). It promotes the elevation of circulating insulin and improves glucose tolerance but can also inhibit the high glucose induced activation of the Insulin Receptor (3, 6, 7). Serpin A12 inhibits TRANCE/RANK L induced osteoclast development and the inflammatory activation of vascular smooth muscle and endothelial cells (7-9). It additionally functions as an anti-apoptotic protein in vascular endothelial cells and osteoblasts (10, 11).

• References:

1. Choi, S.H. et al. (2013) Front. Endocrinol. (Lausanne) 4:97.

2. Goktas, Z. et al. (2013) Front. Endocrinol. (Lausanne) 4:69.

3. Hida, K. et al. (2005) Proc. Natl. Acad. Sci. USA 102:10610.

4. Lee, J.A. et al. (2011) Endocr. J. 58:639.

5. Caminos, J.E. et al. (2009) Histol. Histopathol. 24:979.

6. Heiker, J.T. et al. (2013) Cell Mol. Life Sci. 70:2569.

7. Li, H. et al. (2013} Atherosclerosis 228:61.

8. Kamino, N. et al. (2013) Connect. Tissue Res. 54:147.

9. Jung, C.H. et al. (2014) Cardiovasc. Diabetol. 13:41.

10. Jung, C.H. et al. (2011) Biochem. Biophys. Res. Commun. 413:264.

11. Zhu, X. et al. (2013) Amino Acids 44:961.

• Entrez Gene IDs:

  145264 (Human); 68054 (Mouse); 191570 (Rat)

• Alternate Names:

  antitrypsin), member 12; member 12; OL-64; OL-64Visceral adipose-specific serpin; serine (or cysteine) proteinase inhibitor, clade A (alpha-1 antiproteinase; Serpin A12; serpin peptidase inhibitor, clade A (alpha-1 antiproteinase, antitrypsin); Vaspin; Visceral adipose tissue-derived serine protease inhibitor