Biosynthesis of Pyridine Nucleotides in Early Embryos of the Mouse (Mus musculus)

The diphosphopyridine nucleotide contents of mouse embryos at various stages of development were determined with an enzymic cycling method. These were 0.07 pmole per individual for unfertilized ova and early one-cell embryos and 0.03 to 0.04 pmole per embryo for embryos at all stages from two-cell through blastocyst. There was no concomitant increase in triphosphopyridine nucleotide content on development from the one-cell to the two-cell stage. Growth of two-cell embryos in vitro for 24 hours in the presence of either nicotinamide or nicotinate (0.8 mm) lead to a 2.5-fold increase in diphosphopyridine nucleotide content. Isotopically labeled nicotinamide, nicotinate, and quinolinate, but not tryptophan were incorporated into pyridine nucleotides by embryos cultured in vitro. Azaserine inhibited pyridine nucleotide synthesis from nicotinate but not from nicotinamide. Nicotinate was more rapidly incorporated into the pyridine nucleotides than was nicotinamide, but the total incorporation after 24 hours was the same for both precursors. The extent of the incorporation of labeled nicotinamide into DPN by preimplantation embryos at all stages was nearly constant for any given 24-hour period. A precipitous increase in incorporation occurred subsequent to the hatching of the blastocyst from the zona; it coincided with the beginnings of embryonic growth. The data permit the conclusion that preimplantation embryos are capable of the de novo synthesis of DPN and that deamidation is not an obligatory step in the biosynthesis of DPN from nicotinamide.