The Role of Oil in Protein Crystallization - Molecules: Nucleation, Aggregation and Crystallization - page 132

is heavier than the oil and settles at the bottom of the container. Setting up
batch trials is simpler and speedier than other methods especially when
trials are dispensed automatically (Chayen et al ., 1990, 1992, 1994; Luft
et al ., 2001; DeLucas et al ., 2003).
The IMPAX equipment is usually operated in two main modes: one
mode is used to screen a wide range of crystallization conditions, while
the other generates a matrix survey, to optimize the precise conditions for
obtaining the best crystals.
The IMPAX apparatus was the first robot to dispense microbatch
experiments. Today, there are several devices for doing that (Luft et al .,
2001; DeLucas et al ., 2003; Stock et al ., 2005). A considerable number of
proteins and other macromolecules have been successfully crystallized
using the microbatch technique (e.g. Kleywegt et al ., 1994; Meyer et al .,
2004; Malkowski et al ., 2007).
The utilization of oil for protein crystallization was originally initi-
ated as described above in order to enable the dispensing and incubation
of very small crystallization samples using the microbatch method in
which crystals are grown in nanolitre volume drops of a mixture of a pro-
tein and crystallizing agents. The primary role of the oil was to act as an
inert sealant to prevent evaporation of the small-volume trials.
Experimental evidence has since then revealed that the oil itself can play
an important part in the outcome of a crystallization experiment by
affecting the crystallization process throughout its stages (of nucleation,
growth and the stability of the resulting crystals). A wide scope of exper-
iments which exploit the presence of oil to aid protein crystal growth are
presented. This article focuses on protein crystals, although the methods
described also apply to other biological macromolecules. Figure 2 shows
a view of a 2 l drop under oil containing a crystal of an alcohol dehy-

drogenase (Korkhin et al ., 1996).
The microbatch method is essentially a batch experiment in which
the macromolecule and the crystallizing agents are mixed at their final
concentrations at the start of the experiment; thus, supersaturation is
achieved upon mixing. Consequently, the volume and the composition
of a trial remain constant. This is in contrast to all other crystallization

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