X-tal protocols


Protein Detergent Methods Euipment Screen Drops Reference

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1. Examination of the crystallization experiments.

The drops are first checked at low magnification (40x), then more closely at l00x. Do not use polarized light, because of interference from the plastic tray with the polarized beam. At this stage the color of the precipitate is important.

The results of the crystallization experiments are recorded using the numbering scheme. The score is used to classify the contents of the drop with one or more numbers, to save space in the lab book and for easy identification.

Example: A score of 49 = gelatinous precipitate (score 4) with crystals (score 9).

The scoring is not a quality scoring; a higher number does not necessarily mean a better result.

When screening for crystallisation condition, examine the conditions

  1. immediately after setup
  2. each day for the first week
  3. once a week for several weeks. (store upto 2 years)
The rate of formation is important for optimization of the precipitant concentration.

In the final stages of optimization, when we are aiming for highly ordered, big crystals, it is better not to disturb the crystal growth. Wait one or two weeks before checking the experiment.

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2. Crystallization drop phenomena and interpretation.

The protein is not precipitated. Empty drop

0. The drop is clear.

Drop with glass 1. Drop contains non-protein particles.

Precipitate shows no birefringence and has no edges. Precipitated protein

2. Drop is mostly clear but contains precipitated protein

Precipitated protein 3. Protein fully precipitated

Gelatinous precipitate 4. Gelatinous or particulated precipitate

phase seperation 5. Phase separation

Precipitate shows birefringence or has edges.

spherulites 6. Spherulites or microcrystals

needles 7. Needles

Plates 8. Plates

crystals 9. Crystals

Top Back © 12 Febr. 2004 Johan Zeelen