Albany College of Pharmacy and Health Sciences 2 articles published in JoVE Biochemistry Cell Fractionation of U937 Cells by Isopycnic Density Gradient Purification William D. McCaig1, Matthew A. Deragon1, Phillip V. Truong1, Angeleigh R. Knapp1, Timothy J. LaRocca1 1Department of Basic and Clinical Sciences, Albany College of Pharmacy and Health Sciences This fractionation protocol will allow researchers to isolate cytoplasmic, nuclear, mitochondrial, and membrane proteins from mammalian cells. The latter two subcellular fractions are further purified via isopycnic density gradient. Biochemistry Cell Fractionation of U937 Cells in the Absence of High-speed Centrifugation William D. McCaig1, Matthew A. Deragon1, Robert J. Haluska Jr,1, Alexa L. Hodges1, Payal S. Patel1, Timothy J. LaRocca1 1Department of Basic and Clinical Sciences, Albany College of Pharmacy and Health Sciences Here, we present a protocol to isolate the plasma membrane, cytoplasm and mitochondria of U937 cells without the use of high-speed centrifugation. This technique can be used to purify subcellular fractions for subsequent examination of protein localization via immunoblotting.