The action of bone phosphatase on the esters of phosphoric acid of the blood.

THE presence in bone of an enzy'me capable of hydrolysing organic esters of phosphoric acid to yield inorganic phosphate was demonstrated by Robison [1923]. A considerable body of evidence has since been brought forward by Robison and his co-workers in support of the suggestion that the bone enzyme is intimately concerned in the process of ossification in bone formation. It was suggested that the deposition of bone salts resulted from the hydrolysis by the enzyme (phosphatase) of organic compounds of phosphorus to yield free phosphate, any increase of which would, in the presence of inorganic calcium, lead to precipitation of calcium phosphate. The presence, in the fluid bathing the bone, of a suitable substrate for the phosphatase was, of course, a necessary part of this hypothesis, and Kay and Robison [1924] were able to demonstrate a partial hydrolysis in the presence of the enzyme of the " acid-soluble organic phosphorus " of the blood. Their experiments were carried out on neutralised trichloroacetic acid filtrates of whole blood, on which the bone phosphatase was allowed to act at 370 and at its optimum pHE of about 9. Under these conditions only a fraction (usually about 25 %) of the acid-soluble organic phosphorus compounds present in the blood was hydrolysed by the enzyme. Since dilute solutions of primary esters of phosphoric acid are readily and almost completely hydrolysed by phosphatase in a few hours. it was supposed that in blood there were at least two phosphoric esters, one of which was rapidly hydrolysed by bone phosphatase, while the other was very resistant to the action of the enzyme. In contrast to the limited hydrolysis by enzymic action, almost complete hydrolysis of the acidsoluble phosphorus of blood resulted from boiling with dilute mineral acid. In some experiments in this laboratory on the combined action of phosphatase and lipase on lecithin, an unexpectedly large increase of inorganic phosphorus was observed in control flasks which contained phosphatase, lipase and buffer, but no lecithin. The source of this phosphorus was traced to the lipase preparation, an extract of pig's pancreas, which was found to contain large amounts of acid-soluble phosphorus. It seemed worth while to investi-