Cells of a genetic variant of the hamster fibroblast line BHK 21 which lack inosinic pyrophosphorylase activity {IPP~ cells) and therefore cannot normally incorporate [H]hypoxanthine were grown in mixed culture with cells of BHK 21 sublines which have inosinic pyrophosphorylase activity (IPP cells). If not in contact with IPP cells, 1PP~ cells do not incorporate added [H]hypoxanthine into nucle...

Rates of purine synthesis de novo, as measured by the incorporation of [14C]formate into newly synthesized purines, have been determined in cultured human fibroblasts derived from normal individuals and from patients deficient in adenosine deaminase, purine nucleoside phosphorylase, or hypoxanthine phosphoribosyltransferase, three consecutive enzymes of the purine salvage pathway. All four type...

Comparison of the primary structures of three phosphoribosyltransferases (human hypoxanthine-guanine, Salmonella typhimurium ATP, and Escherichia coli glutamine) showed no significant amino acid sequence homology except for a 35-residue span in hypoxanthine-guanine and glutamine phosphoribosyltransferases. However, comparison of smoothed plots of amino acid physical characteristics thought to c...

The role of DNA modification in the maintenance of mammalian X-chromosome inactivation was investigated by using the technique of DNA transformation in mammalian cells. The ability of inactive X-chromosome DNA from adult mouse tissues to act in transformation for the X-linked hypoxanthine phosphoribosyltransferase gene (Hprt) could be ascertained by utilizing a recently discovered electrophoret...

Photocycloaddition, Thymine, Azetidine, Cyclobutane Adducts Photochemical reactions of thymine linked to hypoxanthine or imidazole by a trimethylene chain were studied in aqueous solution. Irradiation (A = 254 nm) of thymine-hypoxanthine pair yielded two internal cycloadducts with azetidine and cyclobutane part structures. Sensitization and quenching experiments suggested that the excited singl...

9-(4'-Phosphonomethoxy-2'-cyclopenten-1'-yl)hypoxanthine and 9-(4'-phosphonomethoxy-2',3'-dihydroxycyclopenten-1'-yl)hypoxanthine were synthesized as isosteric carbocyclic analogues of inosine-5'-monophosphate. The synthesized compounds were shown to be capable of inhibiting the activity of human type II inosine-5'-monophosphate dehydrogenase (IMPDH II) (IC(50 )= 500 µM) and to have no signific...

Adenine transport in the L1210 leukemia cell is mediated by a rapid facilitated process. Evidence supporting a carrier transport mechanism includes the observations that 1) extracellular hypoxanthine or xanthine inhibits net adenine uptake and 2) the presence of these bases within the intracellular compartment produces an uphill flow of adenine into the cell (countertransport). On the other han...