On weight basis, the percentage of proteins contain in a cell membrane is:

Proteins are major constituents of membranes (~50% by weight in the plasma membrane). Integral proteins are directly incorporated within the lipid bilayer itself, whereas peripheral proteins exhibit a looser association with one of the two membrane surfaces, paicularly the inner. Ref: (2013). Chapter 2. The Cytoplasm. In Mescher A.L. (Eds), Junqueira's Basic Histology: Text & Atlas, 13e.