Studies on the biosynthesis and role of diguanosine tetraphosphate during growth and development of Artemia salina

Abstract

Analysis of the acid-soluble fraction during growth and development of the brine shrimp, Artemia salina, using guanosine- 3H and ionexchange techniques, indicates diguanosine tetraphosphate (Gp 4G) to be peculiar to the female and to be actively synthesized by the developing ovarian egg. Although the diguanosine nucleotides have been detected in other encysted embryos (the water flea, Daphnia magna, and the fairy shrimp, Eubranchipus vernalis), Gp 4G does not appear to be unique to encysted eggs; eggs of the brine shrimp destined to develop ovoviviparously contain similar amounts of Gp 4G. In contrast, diguanosine triphosphate (Gp 3G) is not synthesized during oogenesis but arises during cleavage in encysted embryos at least. The inability of the brine shrimp to incorporate 14C-labeled bicarbonate and/or formate into acid-soluble or nucleic acid purines at all stages of growth and development, whereas the pyrimidine nucleotides in both fractions become heavily labeled, indicates Artemia to be incapable of purine synthesis de novo. This is particularily striking during oogenesis when considerable amounts of Gp 4G are being synthesized. Ostensibly, purine nucleotide synthesis in Artemia requires the presence of a purine ring or closely related derivative; the exact nature of this requirement is now under study. When 3H-labeled adenosine and guanosine are introduced into the medium, rapid incorporation into purine nucleotides occurs. Finally, Gp 4G appears to be the sole source of purines for development.