Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:The various phosphorylated forms of 4E-BP1 (designated , , and ) were separated by SDSPAGE electrophoresis and quantitated by protein immunoblot analysis as described previously (27, 45, 46).
Category: