MetaCyc Enzyme: guanine deaminase

Species: Camellia sinensis

Guanosine deaminase and guanine deaminase were partially purified from tea leaves. The activity of guanosine deaminase is about 28 times higher than that of guanine deaminase, and that the Km of guanosine deaminase for guanosine is lower than that of guanine deaminase for guanine. These indicate that the conversion of guanosine to xanthosine proceeds faster than the conversion of guanine to xanthine.

Molecular Weight of Polypeptide: 54 kD (experimental) [Negishi94 ]

Gene-Reaction Schematic: ?

Gene-Reaction Schematic

Enzymatic reaction of: guanine deaminase

EC Number:

guanine + H+ + H2O <=> ammonium + xanthine

The reaction direction shown, that is, A + B ↔ C + D versus C + D ↔ A + B, is in accordance with the Enzyme Commission system.

The reaction is favored in the direction shown.

In Pathways: superpathway of purines degradation in plants , purine nucleotides degradation I (plants) , superpathway of guanosine nucleotides degradation (plants) , guanosine nucleotides degradation II

Guanine deaminase has double peaks of optimum activity, at pH 7.0-7.5 and pH 8.0.

Inhibitors (Unknown Mechanism): Zn2+ [Negishi94]

Kinetic Parameters:

Km (μM)

T(opt): 40 °C [Negishi94]


Negishi94: Negishi, Osamu, Ozawa, Tetsuo, Imagawa, Hiroshi (1994). "Guanosine deaminase and guanine deaminase from tea leaves." Biosci. Biotech. Biochem. 58(7): 1277-1281.

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Please cite the following article in publications resulting from the use of MetaCyc: Caspi et al, Nucleic Acids Research 42:D459-D471 2014
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