A Fractionation Procedure for the Acid-Soluble Phosphorus Compounds of Liver

A procedure has been worked out for the fractionation of the acidsoluble P compounds of liver for use in tracer experiments. Like all similar fractionations, e.g., those of LePage (6) and Kaplan and Greenberg (3), it is based principally on differences in the solubilities of the alkaline earth salts of these compounds and in their susceptibility to hydrolysis. LePage separates the “barium-insoluble” from the “bariumsoluble” compounds, then applies appropriate analytical methods to each fraction. This is adequate for analytical purposes but does not effect the separation necessary for tracer experiments. Kaplan and Greenberg have carried the separation somewhat further in their tracer studies (4). The present procedure is considered to be an improvement over that of Kaplan and Greenberg in that a more complete separation of the alkaline earth-insoluble compounds from the soluble ones is achieved by the use of calcium in addition to barium than is possible with barium alone. Also, the alkaline earth-soluble fraction has been separated into several well defined entities. The procedure is simpler than would be the case if phosphocreatine were present. Although a number of papers indicate the presence of this substance in liver, there are no reports of its isolation from this organ. When molybdic acid reagent was added at room temperature to liver filtrates from which inorganic P had been removed by magnesia mixture, no indication was obtained of the presence of any readily hydrolyzable P compound corresponding to phosphocreatine. The procedure as given below should be applicable to other mammalian tissues which do not contain phosphocreatine. The fractionation has been applied to tracer studies on the metabolic significance of the phosphorus compounds, on rats of the Carworth and Sprague-Dawley strains. The results of these experiments will be described in a subsequent paper. It may be mentioned that differences were found between these two strains with respect to the amount of total acid-soluble P in the liver and in the amounts of adenylic acid, glucose-6-