Unizer s i t y , Saint Lowis, Missouri
T W O FIQURES
Researches of the past two decades have focused attention on phosphorus metabolism as a matter of paramount importance in the mechanics of living matter. Of especial interest has been the study of adenosinetriphosphate ( A T P ) , for this substance continues to be the only known compound capable of receiving, storing, and transmitting to cellular mechanisms the energy produced by glycolytic and respiratory processes (cf. Lipmann, '41). At first recognized only as an intermediary in glycolysis, A T P has been elevated to a position of more general interest by the work of Colowick, Kalckar, and Cori ('41), who showed that the complete combustion of one mole of glucose leads to the esterification, presumably by way of the adeiiylic acid system, of at least ten moles of inorganic phosphate in excess of what the reaction itself consumes. I n muscle it is probable that the extra ,4TP thus generated supplies energy for the performance of mechanical work (cf. Kalckar, '42) ; and it is a striking fact that muscle adenosinetriphosphatase, the enzyme that catalyzes the energy-yielding dephosphorylation of ATP to adenosinediphosphate, is either identical with myosin or very difficult to separate from it (Engelhardt and Ljubimova, '39; D. M. Needham, '42 ; Bailey, '42 ; Kalckar, '44).
It is probable that A T P promotes numerous cellular functions in addition to muscle contraction, for a substance corresponding to ATP has been identified in numerous tissues besides muscle, and an enzyme capable of splitting the polyphosphate has been recently demonstrated in a variety of rat organs by DuBois and Potter ('43). Thus it seemed of interest to us, in the course of a series of studies on the enzymology of embryos, to determine the adenylpyrophosphatase activity of embryonic tissue, and so to derive an estimate of the extent to which early r ' wrowth and differentiation map depend on energy yielded by ATP.
* Aided by a grant from the Rockefeller Foundation.
Sinre we made no attempt to differentiate between adenosinetripliosphatase and adenosinediphosphatase, we shall follow Kalckar ( ' 4 4 ) in using the common term ( 'adenylpyrophosphatase". We shall also use the abbreviated form "apyrase" suggested by Meyerhof ( '45).