A protocol for liver tissue particularly is not offered. Here is a protocol for tissue in general:
Tissue homogenates are prepared by homogenizing tissue in ice-cold PhosphoSafe extraction buffer using 70 ul buffer/mg tissue. Homogenates are incubated at room temperature for 5 mins, sonicated on ice, and then subjected to centrifugation (spun at 16,000 X g, 5 mins, at 4 Celsius). The resulting supernatant is collected (the end-user will want to keep this, and can discard the insoluble pellet). Finally, protein concentration is determined by a protein assay (e.g., Bradford assay).
To minimize proteolysis, extraction can be performed on ice, and protease inhibitors can be added.
Please see the link below to access the full product user guide:
https://www.emdmillipore.com/product/PhosphoSafe-Extraction-Reagent,EMD_BIO-71296#anchor_USP