Glutamine 5-Phosphoribosyl-l-pyrophosphate

In the enzyme catalysis of the first committed step in the de novo synthesis of purines, an amino group from L-glutamine is transferred to 5-phosphoribosyl-l-pyrophosphate to form glutamate and 5-phosphoribosyl-1-amine. The assay includes glycinamide ribonucleotide synthetase, which converts 5-phosphoribosyl-l-amine to glycinamide ribonucleotide, which is the reaction product quantitated. 

Activity was determined in a 100 (iL reaction mixture containing 10 mM Bicine (pH 8), 50 mM KC1, 3 mM magnesium acetate, 2 mM ATP, 3 mM glycine, 10 mM L-glutamine, 1 mM 5-phosphoribosyl-l-pyrophosphate, 3 to 

5 units of glycinamide ribonucleotide synthetase, and 5 to 30 /u.L of extract. The assay proceeded for 30 minutes at ambient temperature before being stopped by the addition of 100 fiL of acetonitrile-1 M HC1,9 1. The samples were centrifuged for S minutes to remove precipitated proteins before analysis by injection of 25 /mL into the HPLC system. 

The assay was demonstrated to be suitable for measurement of enzyme activity in extracts prepared from Azotobacter vinelandii and soybean nodules. 

Thiopurine methyltransferase S-methylates 6-mercaptopurine and 6-thiogua-nine, both of which are used as antileukemic drugs. The source of the methyl group is 5-adenosyl-L-methionine. 

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Glutamine 5-phosphoribosyl-l-pyrophosphate amidotransferase, 38 310-311 Glutamine phosphoribosylpyrophosphate amidotransferase, ground spin state variability, 38 99-100 Glutathion... 

Fe/S clusters in regulatory enzymes have been proposed to act as sensors in such a manner that, upon detection of a measurand, the cluster disintegrates and activity stops. Putative examples are NO sensing by the [2Fe-2S] cluster in the terminal enzyme of heme synthesis, ferrochelatase [8], and 02 sensing by the [4Fe-4S] cluster in the regulatory enzyme of purine nucleotide biosynthesis, glutamine 5-phosphoribosyl-l-pyrophosphate amidotransferase [9], This is of course not a catalytic activity, since the cluster is destroyed in the action. 

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