I n a recent paper, Steinbach arid Moog ( '45) showed that in homogenates of chick embryos the phosphate-transferring enzyme adenlpyrophosphatase is bound to insoluble granular material which may be separated from cleared water extracts by high speed centrifugation. This work, taken in conjunction with data recently discussed by Stern ('43) and by Lazarow ('43)' appears to substantiate our suggestion that the centrifugable granules are components of a cytoskeleton on which the enzymatic activities of intact cells are oriented. To examine this idea further, we are engaging in a series of studies on the relation of other enzymes to granules isolated from homogenates of developng chick embryos.
The present report deals with the common acid and alkaline phosphomonoesterases in embryos of 7 to 12 days' incubation. During this period, as is shown in the preceding paper (Moog, '46), the over-all activity of the alkaline enzyme (calculated in terms of total nitrogen content) rises to a maximum at about 10 days, but the acid enzyme is almost unchanged. According to an earlier histochemical study (Moog, '44)' the two phosphomonoesterases begin at about 7 days to accumulate at their functional sites in the developing organs. Thus the period under consideration might be expected to yield information about the building up of our previously postulated "activity structure."
Sided by a grunt from the Rockefeller Foundation.