Loss of pH sensitivity of amino acid incorporation during early development of the horseshoe crab, Limulus polyphemus L

Abstract Embryos of the primitive arthropod, Limulus polyphemus L., exhibit a 5–50‐fold increase in amino acid incorporation approximately 6–8 hours after fertilization, which is not concomitant with cytoplasmic alkalization. Lowering of intracellular pH before this increase occurs will prevent the initiation of amino acid incorporation. However, lowering the internal pH after the increase has occurred does not inhibit the incorporation rate. These results suggest that amino acid incorporation in Limulus embryos is a pH‐sensitive event before the increase occurs, but becomes pH insensitive after the increase in incorporation rate has been initiated.