Guanine aminohydrolase

Guanine aminohydrolase is present in a variety of animal tissues (55-58), in lobster hepatopancreas (37), in certain bacteria (59), and... 

Partially purified preparations of guanine aminohydrolase (EC 3.5.4.3) have been reported from rabbit liver (68,186), rat liver (61), Clostridium addwrici (187), rat brain (60, 188, 189), and lingcod muscle (190). The rat brain enzyme (60) occurs in both the mitochondrial and supernatant fraction the latter fraction yielded two forms, A and B from DEAE-cellulose, which were subsequently purified 70- and 600-fold, respectively. Form B had a specific activity of 290 /unoles/min/mg. Kinetic, immunochemical, and electrophoretic studies revealed that the mitochondrial enzyme was distinct from supernatant enzyme B. A distinction between the supernatant A and B forms was less certain (60). 

Little is known of the physical properties of guanine aminohydrolase. Elution of rabbit liver enzyme from Sephadex gave a skewed activity peak the estimated molecular weight of the main component was 170,000, a minor shoulder component, 525,000 (60). 

Since guanine aminohydrolase catalyzes the deamination of thioguanine and 8-azaguanine thereby destroying their anti-neoplastic effects, Baker and his colleagues have prepared a series of active site directed irreversible inhibitors to block the enzyme in tumor tissue (193). The most effective inhibitor, 9-(4-methoxy phenyl)guanine, effected a 50 inhibition at 0.38 nM in the presence of 13.3 juM substrate (194). 

Evaluation of serum guanine aminohydrolase activities has been suggested as a quantitative indication of liver cell damage (196). 

Guanine aminohydrolase (guanine deaminase or guanase), present in liver, brain, and other mammalian tissues, provides another pathway to xanthine, this time from guanine. Subsequent oxidation of xanthine to uric acid then occurs. 

S.4.3 Guanine aminohydrolase Guanine deaminase Guanosine deaminase... 

Purification of jS-o-galactosidase by affinity chromatography Isolation of glycogen phosphorylase B by affinity chromatography Purification of guanine aminohydrolase by affinity chromatography... 

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