Hydrolysis of phosphoric esters by the kidney in vivo

Abstract

Robison (1923) found that aqueous extracts of macerated kidney contain an enzyme which hydrolyses phosphoric esters, such as hexosephosphates and glycerophosphate. This enzyme is also present in bones and teeth, and occurs in cartilage as soon as ossification starts. It is also present in the intestinal mucosa, but other tissues contain it in traces only. It is characterised by a high optimum p H (8·4-9·4). At p H 9·3 its activity is five times as great as at p H 7·3 (Robison and Soames, 1924). It was suggested by Robison that this enzyme plays an important rôle in the calcification of bone, and the suggestion has been supported by a considerable amount of evidence (3, 4, 5). Nothing, however, was known of the function of the enzyme in the kidney. It was thought possible that it might be required for the eventual hydrolysis and excretion of those phosphoric esters, which are present in considerable amount in the red corpuscles and in small amount in the plasma. Eichholtz and Starling (1925) have recently shown that the isolated kidney wheir perfused by means of a heart-lung preparation, does not excrete inorganic phosphates. This disability they attribute to the fact that the inorganic phosphates of the serum are present in a state to which the glomerular membrane is impermeable. They suggest, therefore, that the normal urinary phosphates are secreted by the tubule cells. Moreover, under the conditions of the experiment, the phosphate excretion would seem to be more readily extinguished than the excretion of either urea or sulphate.