Reliable quantification of in vitro synthesized green fluorescent protein: comparison of fluorescence activity and total protein levels.

At any time in vitro or in vivo expressed unlabeled proteins have to be quantified it is difficult to find a reliable method, especially with nonpurified samples. Quantification via protein activity can result in too low levels if the proteins analyzed tend to aggregate into inactive forms. Here, wild-type green fluorescent protein (GFPwt) was expressed in high amounts in vitro using the Rapid Translation System 500 based on Escherichia coli lysates.