STUDIES ON THE UREASE OF THE EGGS AND EMBRYOS OF THE SEA URCHIN, STRONGYLOCENTROTUS PURPURATUS

Abstract

1. The urease activity of sea urchin eggs and embryos has been followed in vitro to the pluteus stage. The activity was found to decline by about 30% upon reaching the blastula stage, after which it remains relatively constant. 2. Adult sea urchin tissues were found to contain urease of activity comparable to that of the eggs and embryos. 3. The in vivo activity of urease in fertilized and unfertilized eggs was compared, with little or no change on fertilization noted. 4. The in vivo activity was found to be considerably lower than in vitro activity when measured under the same conditions, and evidence indicates that the in vivo activity is limited, at least in part, by the rate of penetration of urea into the eggs. 5. Of the enzymes usually involved in the formation of urea from purines, xanthine oxidase, uricase, allantoinase and allantoicase are shown to be present in sea urchin eggs, whereas adenase was not demonstrable with the method employed. 6. No ammonia within the range detectable by the methods employed was liberated into sea water by embryos during the periods of 20 minutes to 12 hours after fertilization, and 24 hours to 60 hours after fertilization. 7. The results suggest that urease and the related enzymes function to add nitrogen from purines to the metabolic ammonia pool during the pre-feeding stages of development.