Membrane differentiation and de novo synthesis of the (Na+ + K+)-activated adenosine triphosphatase during development of Artemia salina nauplii

The developing brine shrimp, Artemia salina, nauplius is explored as a new model for the study of the biogenesis of the cation transport enzyme, (Na+ + K+)-activated adenosine triphosphatase [(Na, K)-ATPase]. (Na, K)-ATPase activity develops from undetectable levels in preemergent cysts (embryos prior to 12 hr of development) to very high levels in the nauplius after 40 hr of incubation in sea water [Conte, F. P., Droukas, P. C., and Ewing, R. D. 1977). J. Exp. Zool. 202, 339], then declines between 44 and 72 hr. Similar ontogenic patterns of enzyme activity development are observed for Mg-ATPase, 5′-nucleotidase, glucose-6-phosphatase, NADH oxidase (rotenone insensitive), and cytochrome oxidase. However, these enzymes show measurable activity in the early cyst stage, and the points at which the activity increases and then reaches a maximum are usually different from those of the (Na, K)-ATPase. These enzyme ontogeny studies demonstrate that membrane differentiation is extensive during the period in naupliar development when (Na, K)-ATPase activity appears, and that the appearance of specific enzymes is asynchronous during embryogenesis. Pulse-chase experiments with NaH14CO3 show an increase in the specific radioactivity of the partially purified (Na, K)-ATPase which is maximum when the label is administered at 12–18 hr after the initiation of development. At this time the specific radioactivity increases with purity of the enzyme, whereas in earlier pulse periods the specific radioactivity is higher in the more crude enzyme fractions, suggesting that preferential synthesis of the (Na, K)-ATPase occurs between 12 and 18 hr. Radioactivity is found in the subunits of the partially purified (Na, K)-ATPase isolated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and is maximum for the 12- to 18-hr pulse experiment. These pulse-chase experiments demonstrate that the large increase in (Na, K)-ATPase activity is due to de novo synthesis and establish that the brine shrimp is a workable new model for the study of the biogenesis of the (Na, K)-ATPase.