Metabolic Functions of Myo-inositol III. UTILIZATION OF PURINE BASES AND NUCLEOSIDES FOR NUCLEIC ACID BIOSYNTHESIS IN INOSITOL-DEFICIENT KB CELLS

Abstract The ability of inositol-deficient KB cells to use purine bases and nucleosides for the biosynthesis of nucleotides and nucleic acids was studied with the aid of 8-14C-adenine and 8-14C-guanosine. The rate of incorporation of 8-14C-adenine into the ribonucleic acid of deficient cells was at least 50% of the normal value even though the specific activities of the RNA bases were the same as those of normal cells. When 8-14C-guanosine was the radioactive precursor, the rate of labeling of the acid-soluble guanine and adenine nucleotides of deficient cells was one-half of that of normal cells. Similarly, the rate of incorporation of 8-14C-guanosine into RNA guanine and adenine of the deficient cells was 25% and 37%, respectively, of the normal rate. As a consequence of this, the specific activities of the RNA bases of the deficient cells were lower than those of normal cells. In the presence of nucleotide precursors, cells grown without inositol showed a decreased rate of cell division while maintaining approximately a normal rate of nucleic acid biosynthesis. This results in cells containing increased levels of nucleic acids. The levels of guanase and nucleoside phosphorylase activities of deficient cells were the same as those of normal cells, but the level of guanosine 5'-phosphate pyrophosphorylase activity was reduced to 40% of the normal value. The loss of intracellular purine compounds into the culture fluid was very small, and it was the same in both types of cells. It is concluded that inositol-deficient cells are unable to incorporate adenine and guanosine into the nucleic acids at a normal rate, and that inositol deficiency affects more the metabolism of guanosine by causing a decrease of the level of GMP pyrophosphorylase activity.