THE DETERMINATION OF INORGANIC PHOSPHATE IN THE PRESENCE OF LABILE PHOSPHATE ESTERS

Abstract

Labile phosphate esters such as phosphocreatine, acetyl phosphate, and ribose-l-phosphate (1) have assumed great biological importance. These esters are so unstable that they are split with great rapidity by the reagents commonly used for inorganic phosphate determination. Therefore, the usual inorganic phosphate measurements in tissue extracts, etc., actually represent the sum of the inorganic phosphate and the phosphate of these labile esters. In order to determine the labile esters it has usually been necessary to perform a prior removal of inorganic phosphate by precipitation (2). By working very rapidly, Fiske and Subbarom (3) were able to measure inorganic phosphate in the presence of phosphocreatine, but, due to the speed of the reaction, this procedure has been difficult to use. The detection and determination of such esters would become very simple if it were possible to determine inorganic phosphate in their presence, since the labile phosphate could then be measured by the inorganic phosphate liberated as the result of very mild hydrolysis. It has been found possible to establish conditions under which inorganic phosphate can readily be determined in the presence of labile esters. In addition to describing the procedure, data are presented as to the speed of hydrolysis of several of the labile esters under the prescribed conditions.