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Ubiquinone and vitamin K show a characteristic distribution among bacterial species (Bishop, Pandya & King, 1962). Neither is present in cells lacking aerobic respiration. Otherwise, Grampositive organisms contain vitamin K but not ubiquinone, and Gram-negative organisms contain ubiquinone but not vitamin K, except for a few types (e.g. Eacherichia coli, Proteu8 vulgari8) which contain both. The interspecific distribution of these substances would thus suggest that they play a part in respiratory processes, as has been suggested for animal tissues (Wolstenholme & O'Connor, 1961). The sites of oxygen utilization and energy production are, in animal tissues, the mitochondria, but bacteria contain no analogous structures. Instead, the electron-transport enzymes appear to be located in the cell membrane (Marr & Cota-Robles, 1957; Mitchell & Moyle, 1956; Nakada, Nozu & Kondo, 1958; Weibull, Beckman & Bergstrom, 1959). This paper presents evidence that vitamin K and ubiquinone are similarly located. Techniques for studying the intracellular distribution of cell constituents are less highly developed for bacterial than for mammalian cells. Three methods are employed here: (a) Disruption of the cells by freezing and the sudden application of high pressures (Hughes, 1951). The soluble cell contents escape leaving the cell walls with the membranes attached. (b) Ultrasonic disintegration, which not only breaks open the cells but also disrupts the 'hulls', i.e. the cell walLs with the membranes attached. The hulls break down only on prolonged treatment to yield particles too small to be precipitated by centrifuging at moderate speed. This forms the basis of the method of 'differential release' described by Marr & Cota-Robles (1957). When a bacterial suspension is subjected to ultrasonic treatment the fall in cell count and fall in turbidity are both exponential but the time-constants are different. If a cell constituent is located entirely in the soluble contents of the cell its release from the

Ubiquinone and vitamin K in bacteria. 2. Intracellular distribution in Escherichia coli and Micrococcus lysodeikticus