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Literature summary for 2.4.2.8 extracted from

  • Page, J.P.; Munagala, N.R.; Wang, C.C.
    Point mutations in the guanine phosphoribosyltransferase from Giardia lamblia modulate pyrophosphate binding and enzyme catalysis (1999), Eur. J. Biochem., 259, 565-571.
    View publication on PubMed

Cloned(Commentary)

Cloned (Comment) Organism
functional overexpression of wild-type enzyme and expression of mutants in Escherichia coli Giardia intestinalis

Protein Variants

Protein Variants Comment Organism
A72G site-directed mutagenesis, exchange in diphosphate binding site, decreased Km-value for diphosphate and guanine, increased Km-value for 5-phosphoribosyl 1-diphosphate, reduced activity Giardia intestinalis
G71A site-directed mutagenesis, no activity Giardia intestinalis
G71E site-directed mutagenesis, no activity Giardia intestinalis
G71R site-directed mutagenesis, no activity Giardia intestinalis
T70K site-directed mutagenesis, exchange in diphosphate binding site, 6.7fold lower Km-value for diphosphate, lower Km for guanine, 2fold increase in Km-value for 5-phosphoribosyl 1-diphosphate, reduced activity Giardia intestinalis
T70K/A72G site-directed mutagenesis, exchange in diphosphate binding site, decreased Km-value for diphosphate and guanine, increased Km-value for 5-phosphoribosyl 1-diphosphate, reduced activity Giardia intestinalis

Inhibitors

Inhibitors Comment Organism Structure
5-phospho-alpha-D-ribose 1-diphosphate competitive against GMP; product inhibition Giardia intestinalis
GMP competitive against 5-phospho-alpha-D-ribose 1-diphosphate; product inhibition Giardia intestinalis

KM Value [mM]

KM Value [mM] KM Value Maximum [mM] Substrate Comment Organism Structure
additional information
-
additional information Km-values of mutant enzymes Giardia intestinalis
0.016
-
guanine wild-type enzyme Giardia intestinalis
0.0225
-
GMP wild-type enzyme, reverse reaction Giardia intestinalis
0.026
-
5-phospho-alpha-D-ribose 1-diphosphate wild-type enzyme Giardia intestinalis
0.324
-
diphosphate wild-type enzyme, reverse reaction Giardia intestinalis

Metals/Ions

Metals/Ions Comment Organism Structure
Mg2+
-
Giardia intestinalis

Organism

Organism UniProt Comment Textmining
Giardia intestinalis
-
-
-

Purification (Commentary)

Purification (Comment) Organism
recombinant wild-type enzyme and mutants from Escherichia coli Giardia intestinalis

Reaction

Reaction Comment Organism Reaction ID
IMP + diphosphate = hypoxanthine + 5-phospho-alpha-D-ribose 1-diphosphate ordered bi-bi mechanism Giardia intestinalis

Substrates and Products (Substrate)

Substrates Comment Substrates Organism Products Comment (Products) Rev. Reac.
guanine + 5-phospho-alpha-D-ribose 1-diphosphate absolutely specific for guanine Giardia intestinalis GMP + diphosphate diphosphate binds at Thr70, diphosphate-binding loop sequence: LTGA r
hypoxanthine + 5-phospho-alpha-D-ribose 1-diphosphate no activity with hypoxanthine Giardia intestinalis IMP + diphosphate
-
?
xanthine + 5-phospho-alpha-D-ribose 1-diphosphate no activity Giardia intestinalis XMP + diphosphate
-
?

Temperature Optimum [°C]

Temperature Optimum [°C] Temperature Optimum Maximum [°C] Comment Organism
37
-
assay at Giardia intestinalis

Turnover Number [1/s]

Turnover Number Minimum [1/s] Turnover Number Maximum [1/s] Substrate Comment Organism Structure
additional information
-
additional information kcat of mutant enzymes Giardia intestinalis
5.7
-
guanine wild-type enzyme Giardia intestinalis
5.8
-
GMP wild-type enzyme, reverse reaction Giardia intestinalis
74.8
-
5-phospho-alpha-D-ribose 1-diphosphate wild-type enzyme, forward reaction Giardia intestinalis
76.7
-
guanine wild-type, forward reaction Giardia intestinalis

pH Optimum

pH Optimum Minimum pH Optimum Maximum Comment Organism
7.5
-
assay at Giardia intestinalis

Ki Value [mM]

Ki Value [mM] Ki Value maximum [mM] Inhibitor Comment Organism Structure
additional information
-
additional information kinetics for product inhibition in forward and reverse reaction, wild-type enzyme Giardia intestinalis