Discussion

The preparation ideally results in large rectangular crystals as seen in Fig. 2. However, the final quality, size and shape of the crystals depend on yet unknown factors. It is not clear how to avoid the many shards of crystals seen in Fig. 3, the oddly shaped crystals in Fig. 4, or clumps of crystals in Fig. 5. Using a low concentration of catalase to crystallize the protein (the concentration given in this protocol) gives larger crystals than a high concentration of protein, which seems to increase the number of shards of crystals. A low concentration of catalase may also minimize clumping of the crystals. The quality of crystals may also depend on the length of dialysis and on the time the crystals are allowed to settle out after dialysis.

Figure 3. Crystals mixed with shards of crystals. Bar, 5 mm.	Figure 4. Crystals with rough edges.
Figure 5. A clump of crystals.

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