Phosphoprotein phosphatase, a new enzyme from the frog egg

In the nutrition of the young, the role of phosphoproteins is, without doubt, an important one. As casein in milk, or as the yellow yolk of many vertebrate and invertebrate eggs, phosphoprotein occurs in substantial quantities. In the frog egg, for example, the yolk platelets occupy almost half the volume of the cell. According to McClendon (5), the yolk of the frog egg consists of phosphoprotein bound to lipide; thus the platelets are a ready source of protein, lipide, and phosphorus. And yet, in spite of the obvious importance of phosphoprotein, little information is available about the manner of its utilization by the developing embryo. It has been assumed that ordinary proteolytic enzymes degrade the protein, and that ordinary phosphomonoesterases split the phosphate from phosphopeptone or from phosphoserine. In the course of an investigation of the distribution of enzymes in the frog egg, a new enzyme (or enzymes) was discovered which is apparently capable of splitting inorganic phosphate from the intact protein molecule. It is the purpose of this paper to present the experiments which led to this conclusion.