Reference

Guanosine-5'-triphosphate,3'-diphosphate 5'-phosphohydrolase purification and substrate specificity

Guanosine-5'-triphosphate,3'-diphosphate 5'-phosphohydrolase purification and substrate specificity. Hara, Akira; Sy, Jose (Lab. Biol. Chem., Rockefeller Univ., New York, NY 10021, USA). Meijo Daigaku Nogakubu Gakujutsu Hokoku, 19, 30-9 (English) 1983. CODEN: MDNGBZ. DOCUMENT TYPE: Journal CA Section: 7 (Enzymes) The regulatory nucleotide guanosine-5'-diphosphate,3'-diphosphate (ppGpp) and its precursor guanosine-5'-triphosphate,3'-diphosphate (pppGpp) are known to be accumulated during the stringent response in bacterial cells. In the present study, the enzyme pppGpp 5'-phophohydrolase (I), which catalyzes the conversion of pppGpp to ppGpp, was partially purified from Escherichia coli. It has a mol. wt. of 140,000 and an apparent Km of 0.11 mM for pppGpp. It requires Mg2+ and a monovalent cation. NH4+ is preferred over K+, whereas Na+ is inactive. The enzyme does not hydrolyze GTP, ATP, pppApp, or ppGpp. Also, it is not effectively inhibited by these nucleotides. I hydrolyzes the 3'-monophosphate analog pppGp equally well (apparent Km of 0.13 mM), yielding the recently identified MS III nucleotide (ppGp). I does not have RNA 5'-terminal-g-phosphatase activity, but 5'-terminal phosphates are released by I when the GTP-terminated RNA chains are first converted into oligonucleotides by RNase A treatment. I actively hydrolyzes the dinucleotide fragment pppGpNp but exhibits very low activity toward longer chain fragments. The 3'-unphosphorylated dinucleotide pppGpN was, however, not hydrolyzed. The ability of I to hydrolyze pppGpp, pppGp, and pppGpNp, but not pppG and pppGpN, indicates that I is rather nonspecific toward the substrate 3'-OH substitutions, although a free, unsubstituted phosphate group at the 3'-OH position is essential.Except for chemicals metioned above, 85130-44-5 and 38918-96-6 are also used. .

Nucleoside utilization by S and G1 cells

Nucleoside utilization by S and G1 cells. Rigau-Lloveras, J.; Olive-Morros, E.; Rivera-Fillat, M. P.; Grau-Oliete, M. R. (Inst. Farmacol., CSIC, Barcelona, Spain).Some commonly used reagents like 73-40-5 and 58-63-9 are used in this experiment. Adv. Exp. Med. Biol., 165A(Purine Metab. Man - 4, Pt. A), 493-6 (English) 1984. CODEN: AEMBAP. ISSN: 0065-2598. DOCUMENT TYPE: Journal CA Section: 13 (Mammalian Biochemistry) The metab. of guanosine at different extracellular concns. of guanosine (1-1000 mM) was studied in L-5178Y murine leukemic lymphoblasts in the S-phase and G1-phase of the cell cycle. Guanosine uptake was greater in S-phase than in G1-phase at all extracellular guanosine concns. Nucleotide formation (anabolism) and incorporation of guanosine into the acid-insol. fraction decreased with increasing guanosine extracellular concns. in both phases, but was greater in the S-phase. Inosine, guanine, and xanthine formation (catabolism) generally increased in both phases with increasing extracellular guanosine and was greater in G1-phase possibly due to lower guanine phosphoribosyltransferase activity. At all times, in both phases, anabolism predominated over catabolism. .