The Enzymology of Feedback Inhibition of Glutamine Phosphoribosylpyrophosphate Amidotransferase by Purine Ribonucleotides

8-Azaguanine Resistance in Mammalian Cells I. Hypoxanthine-Guanine Phosphoribosyltransferase

“…Alterations in the regulation of de novo purine biosynthesis could also bring 25 0 F. D. GILLIN et al about the observed changes in exogenous hypoxanthine utilization characteristic of our mutants. The first enzyme of de novo purine biosynthesis, glutamine: phosphoribosylpyrophosphate amidotransferase (EC 2.42.14) is inhibited by purines (WYNGAARDEN and ASHTON 1959;CASKEY, ASHTON and WYNGAARDEN 1964) and purine analogue ribonucleotides (MCCOLLISTER, GILBERT and ASHTON 1964), and is the site of feedback control for the de novo purine biosynthetic pathway. An 8-AG-resistant mutant of Schizosaccharomyces pombe ( NAGY 1970) which appears defective in amidotransferase feedback inhibition has now been identified.…”

Amidophosphoribosyltransferase

“…<1, 2, 5-9, 11> [3,7,10,13,16]) [3,4,7,10,13,16] P 5-phospho-b-d-ribosylamine + diphosphate <1, 2, 5-9, 11> [3,4,7,10,13,16] Substrates and products S l-glutamine + 5-phospho-a-d-ribose 1-diphosphate + H 2 O <1-12> (<6> reaction at 33% the rate of amminotransferase activity [14]; <11> reaction at 50% the rate of aminotransferase activity [16]; <2> reaction at 70% the rate of aminotransferase activity [11]; <6> glutamine binding site distinct from NH 3 -site [10]; <6> no activity with carbamoyl phosphate [14]) (Reversibility: ? <1, 2, 4-7, 9-12> [3,10,11,14,16,17,27]; ir <3, 8> [2,6]) [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]…”

“…98% inactivation of amidotransferase activity after 30 min [3]; <6> competitive vs. glutamine, inactivation half-life: 11 min [14]) [3,14] 6-iodopurine <6> (<6> 5 mM, 39% inhibition [13]) [13] 6-mercaptopurine ribonucleotide <6> (<6> 5 mM, 64% inhibition [13]) [13] ADP <1, 2, 3, 6, 8, 13> (<3> 1 mM, approx. 95% inhibition [6]; <6> 5 mM, 40% inhibition [13]; <2> 50% inhibition of wild-type, S283A, K305Q, R307Q and S347A mutant enzyme at 4.7 mM, 24 mM, 31 mM, 28 mM and 8.1 mM respectively [25]; <13> 4.1 mM, 50% inhibition [28]) [1,3,6,13,25,28] AMP <1, 2, 3, 4, 6, 7, 8, 9, 10, 11, 13> (<1> approx. 10 mM, complete inhibition, sigmoidal inhibition curve, competitive vs. 5-phospho-a-d-ribose 1-diphosphate, GMP and AMP together have a synergistic effect on inhibition [3]; <3> 1 mM, approx.…”

“…40% inhibition [6]; <9> no inhibition in the presence of 5-phospho-a-d-ribose 1-diphosphate at high concentrations [7]; <6> 1.8 mM, 50% inhibition [8]; <6> 5 mM, 76% inhibition, noncompetive vs. glutamine [13]; <6> 5 mM, 79% and 24% inhibition of aminotransferase and amidotransferase activity at 1 mM 5-phospho-a-d-ribose 1-diphosphate [14]; <11> competitive vs. 5-phospho-a-d-ribose 1-diphosphate [16]; <10> 2.7 mM and 1.2 mM, 50% inhibition of stable and unstable enzyme preparation respectively [17]; <4> 5 mM, 50% inhibition [18]; <1> 4.7 mM, 50% in-hibition [19]; <7> competitive vs. 5-phospho-a-d-ribose 1-diphosphate, noncompetitive vs. glutamine [24]; <2> 50% inhibition of wild-type, S283A, K305Q, R307Q and S347A mutant enzyme at 0.9 mM, 6.1 mM, 2.5 mM, 2.6 mM and 1.5 mM respectively [25]; <13> 6.12 mM, 50% inhibition [28]) [1,3,6,7,8,13,14,16,17,18,19,24,25,28] ATP <6, 8> (<6> 5 mM, 21% inhibition [13]) [1,13] CMP <6> (<6> 5 mM, 22% inhibiiton [13]) [13] GDP <1, 3, 6, 8, 13> (<3> 1 mM, approx. 75% inhibition [6]; <6> 5 mM, 40% inhibition [13]; <13> 8.5 mM, 50% inhibition [28]) [1,3,6,13,28] GMP <1, 2, 3, 4, 6, 8, 9, 10, 11, 13> (<1&...…”

“…<5> Cricetulus griseus [10] <6> Homo sapiens [8,10,13,14,29] <7> Mus musculus [10,24] <8> Columba livia (pigeon [1]) [1,2,10,12] <9> Rattus norvegicus [1,7,10] <10> Schizosaccharomyces pombe (wild type strain 972hand mutant strain ade 2hdevoid of adenylosuccinate synthase [17]) [17] <11> Glycine max (soybean, Merr. cv.…”