To perform in vitro analysis , a protein must be purified away from other cellular components . This process usually begin with cell lysis , in which a cell 's membrane is disrupted and its internal contents released into a solution known as a crude lysate . The resulting mixture can be purified using ultracentrifugation , which fractionates the various cellular components into fractions containing soluble proteins ; membrane lipids and proteins ; cellular organelles , and nucleic acids . Precipitation by a method known as salting out can concentrate the proteins from this lysate . Various types of chromatography are then used to isolate the protein or proteins of interest based on properties such as molecular weight , net charge and binding affinity . The level of purification can be monitored using various types of gel electrophoresis if the desired protein 's molecular weight and isoelectric point are known , by spectroscopy if the protein have distinguishable spectroscopic features , or by enzyme assays if the protein have enzymatic activity . Additionally , proteins can be isolated according their charge using electrofocusing .