A simple method is described that allows a rapid separation of a cell-sap fraction from the large-particle fraction of rat liver suspensions. The method is based on the filtration under suction of liver suspensions through Millipore filters that retain nuclei, mitochondria and some of the endoplasmic-reticulum fraction, but allow quantitative passage of cell sap into a collecting tube. The cell sap may be separated in this manner within 2min of the death of the rat. The method was applied to study the intracellular distribution of ATP and of the nicotinamide–adenine dinucleotides and the results obtained were compared with those obtained after separating the cell sap by a rapid centrifuging procedure. The percentage of total liver ATP in the cell sap was found to be 46% by the filtration method and more than 70% by the centrifuging procedure. Corresponding figures found for the distribution of NADP++NADPH were 40 and 49% respectively.
