These secretory protein would be used for relative expression studies.
You can use spin dialysis (for instance centricon filters) to concentrate the proteins in the medium without having to precipitate (and loose activity). Essentially, you pipet the diluted culture medium into the filter, centrifuge it, and water + solutes below a certain molecular weight (i.e. 10 kDa) pass through the filter, larger proteins stay in the medium on top of the filter in a more concentrated form. Use a refrigerated centrifuge to avoid proteolysis, fungi secrete loads of hydrolases. You can easily concentrate 2 ml of medium to just 200 microlitres in half an hour, that is a 10-fold concentration. The filters come in different sizes and different molecular weight cut-offs (3 kDa, 10 kDa, 30 kDa...)
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