Urease

Urease is an enzyme that converts urea into ammonia.

Uses

Urease autocatalyzes the conversion of urea to ammonia

CO(NH₂)₂ + H₂O

{urease

→

}

2 NH₃ + CO₂

• Optimal catalytic activity occurs at approximately 30°C and pH of 7.4-8.0.
• In a perfectly pure sample, 1g of urease will produce 100g of ammonia nitrogen from urea in 5 minutes at 20°C.

Natural occurrence

• Bacteria and fungi produce urease
• Urease is present in several types of plant seeds (watermelon, pea, and bean)

Character

• For jack bean urease
  • Optimal temperature: 60 °C
  • Optimal pH 6.0

Production

Extraction

Since urease is soluble in propanone, a solvent with a very high vapor pressure, most extractions salve biomass containing urease in propanone, filter and evaporate. The entire process is carried out at low temperatures, often 2-4°C

The source is typically freshly germinated seeds: pea seeds, dehusked watermelon seeds, or jack bean meal.

Catalytic solution

1. Combine 160cc of dry propanone with 340cc of distilled water
2. Mix in 100g of seed pulp
3. Filter, discard residue
4. Dry until all scent of propanone is gone
5. (If necessary) add water to dissolve any precipitate
6. The solution may be added to sources of urea to convert them to ammonia

Purification

Materials

Citric acid buffer: Solution of sodium citrate with 4% w/w citric acid

Phosphate neutral buffer: Solution of KH₂PO₄ with 150% w/w Na₂HPO₄

Process

Repeat:

1. Combine 5% v/v acid buffer with solution
2. Add propanone dropwise until it becomes slightly cloudy
3. Stand overnight
4. Centrifuge at 0° for 30 min
5. Filter, discard filtrate

   The residue is crystals of urease.

6. IF (the crystals are sufficiently homogeneous) THEN exit loop
7. Dissolve residue in neutral buffer solution
8. Centrifuge
9. Retain clear fluid

See Also

• urea
• urine
• ammonia
• Gorin, G. (1965) "Urease. V. Some observations on the procedure for its isolation.".
  Biochim.Biophys.Acta. 99; pp418. 
• Schlegel, H.G.; Kaltwasser, H. (1962) "Urease".; pp1081.
• Sumner, J.B.; Hand, D.B. (1929) "THE ISOELECTRIC POINT OF CRYSTALLINE UREASE".
  J.Am.Chem.Soc. 31