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The zonal ultracentrifuge was used to separate the subcellular components of rat liver brei into soluble phase, microsomal, mitochondrial, membranous fragments, and nuclear fractions during a single centrifugation. The centrifuge was run at 10,000 to 30,000 RPM for 15 to 240 minutes, and the rotor contained a 1200 ml sucrose gradient, varying linearly with radius from 17 to 55 per cent sucrose with a "cushion" of 66 per cent sucrose at the rotor edge. The distribution of the mitochondria was determined using cytochrome oxidase as the marker enzyme. An automated assay system for cytochrome oxidase was developed utilizing reduced cytochrome c as substrate, modules of the Technicon Autoanalyzer, and the Beckman DB Spectrophotometer. All of the cytochrome oxidase activity was restricted to a single peak in the gradient, and no activity could be detected in the zones occupied by the microsomes and nuclei. The mitochondrial fraction was isolated from rat liver brei in 0.25 M sucrose by differential centrifugation, and then run in the zonal ultracentrifuge.This fraction behaved in the zonal ultracentrifuge in the same way as mitochondria separated directly from intact brei. Observations of the isolated fractions in the phase contrast microscope indicated that a wide variety of granules was present in the mitochondrial zone in addition to the true mitochondria. Under the conditions employed, the mitochondria were sedimented essentially to their isopycnic position in the gradient at approximately 43.8 per cent sucrose, density 1.20 gm/cc.

The zonal ultracentrifuge has been used to separate the major components of rat liver brei (soluble phase, ribosomes, microsomes, mitochondria, membranous fragments, and nuclei) during one centrifugation, by using a 1200 ml sucrose gradient varying linearly with radius from 17 to 55 per cent (w/w) with a "cushion" of 66 per cent sucrose at the rotor edge at speeds up to 30,000 RPM. Liver brei was found to contain a family of phosphatases (phenol disodium phosphate substrate, sodium malonate buffers and Turgitol NPX, a non-ionic detergent). Activity maxima at pH 4.1 and 5.9 were observed in untreated brei prepared in 0.25 M sucrose. The addition of the non-ionic detergent Turgitol NPX selectively caused the release of considerable additional activity between these optima. The activity measured at pH 4.1 was primarily associated with the cytoplasmic granules, while the activities at pH 4.8, 5.4 and 5.9 were found in both soluble phase and particulate-mitochondria and membranous fractions. The activities present beyond the region of the gradient occupied by the soluble phase (sample layer) were all bound to particles sedimentable at 105,536 g (average) in the preparative ultracentrifuge. The data suggest that the different activities are not similarly distributed between soluble phase and particulate fractions. When the data are expressed in terms of specific activity, the area in the gradient between the microsomes and mitochondria now appears richest in all the acid phenyl phosphatase activities measured, while the soluble phase and larger particulate fractions appear relatively poor in activity. This part of the gradient is occupied by small, dense granules which may be the so called lysosomes. Pretreatment of the brei with Turgitol NPX prior to fractionation in the zonal ultracentrifuge resulted in the solubilization of acid phenyl phosphatase activities (almost all the activity was in the sample zone of the gradient) and the non-specific destruction of the formed elements of the brei. Essentially all of the activities present in the original brei measured under these conditions were recovered after zonal ultracentrifuge fractionations.