Abstract
Summary
1. DON and azaserine interrupt the development of sand-dollar embryo at mid-blastula and early gastrula stages. The minimum dose of DON producing consistent effects is 3 milligamma/10 cc of sea-water; azaserine is approximately 1/32 as active. Large doses of DON up to 1 mg/10 cc of sea-water have no appreciable effect on fertilization, cleavage or early development. 2. Various physiological purines and derivatives will protect against the action of DON and azaserine, even when added up to 12 hours after fertilization. The most active ones are guanine, hypoxanthine and inosine. The protective action of these substances appears to be non-competitive, and they are not effective against large doses of DON and azaserine. 3. In view of the fact that DON and azaserine, acting as glutamine antagonists, apparently interrupt the de novo synthesis of purines, it is suggested that embryonic development in the sand-dollar is blocked at the time when DNA production, initially supplied by endogenous purine precursors, becomes dependent on de novo purine synthesis.
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