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Biol Bull 122: 232-251. (April 1962)
© 1962 Marine Biological Laboratory
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LOCALIZATION AND PROPERTIES OF PHOSPHOPROTEIN PHOSPHATASE IN THE FROG EGG AND EMBRYO

SYLVAN NASS 1

1 Department of Biology, University College of Arts and Science, New York University, New York 53, New York

1. The phosphoprotein phosphatase activity of various centrifugal fractions and extracts of homogenates of frog ovaries and embryos was studied in the presence and absence of added phosphoprotein substrates and as a function of a number of environmental variables, including incubation time, pH, temperature and ionic concentrations.

2. Yolk prepared in low ionic strength media was far more stable than yolk extracted from whole homogenates with concentrated salt solutions followed by precipitation by dilution or dialysis. The latter fraction lost its characteristic euglobulin properties during preparation, and this was correlated with the loss of phosphoprotein phosphorus from this material.

3. The rate of endogenous P1 release from yolk platelets was found to be a function of the rate of solubilization of the platelets, and the rate of P1 release was linear only as long as the rate of increase of water-soluble protein was linear.

4. The pigment-containing centrifugal fraction was found to have the highest PPPase activity when ovarian fractions were incubated in the presence of added phosphoproteins. Evidence is presented that the activity found in other centrifugal fractions and extracts is a result of varying degrees of pigment contamination.

5. It was found possible to study the enzyme characteristics of PPPase with the enzyme in solution and in the absence of endogenous substrate.

6. Yolk extracts from embryos were far more stable after re-precipitation by water than similarly prepared ovarian extracts. The enzyme activity of the pigment-containing fraction was found to drop precipitously after fertilization, slowly increase from gastrulation to neurulation and rise to a maximum at tailbud. The activity declined after hatching.

7. The possible sources of the discrepancies in the literature concerning the site of PPPase and the composition of yolk proteins are discussed. The significance of the localization studies and the variations in enzyme activity found during embryogenesis is discussed in relation to the morphological changes occurring during that period.






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