Escherichia coli 6-pyruvoyltetrahydropterin synthase ortholog encoded by ygcM has a new catalytic activity for conversion of sepiapterin to 7,8-dihydropterin.
The putative gene (ygcM) of Escherichia coli was verified in vitro to encode the ortholog of 6-pyruvoyltetrahydropterin synthase (PTPS). Unexpectedly, the enzyme was found to convert sepiapterin to 7,8-dihydropterin without any cofactors. The enzymatic product 7,8-dihydropterin was identified by HPLC and mass spectrometry analyses, suggesting a novel activity of the enzyme to cleave the C6 side chain of sepiapterin. The optimal activity occurred at pH 6.5-7.0. The reaction rate increased up to 3.2-fold at 60-80 degrees C, reflecting the thermal stability of the enzyme. The reaction required no metal ion and was activated slightly by low concentrations (1-5 mM) of EDTA. The apparent K(m) value for sepiapterin was determined as 0.92 mM and the V(max) value was 151.3 nmol/min/mg. The new catalytic function of E. coli PTPS does not imply any physiological role, because sepiapterin is not an endogenous substrate of the organism. The same activity, however, was also detected in a PTPS ortholog of Synechocystis sp. PCC 6803 but not significant in Drosophila and human enzymes, suggesting that the activity may be prevalent in bacterial PTPS orthologs.
Woo
Hyun Joo
HJ
Department of Microbiology, Inje University, 621-749, Kimhae, South Korea.
Hwang
Yoon Kyung
YK
Kim
Yeon Jung
YJ
Kang
Jee Yun
JY
Choi
Yong Kee
YK
Kim
Chun Gyu
CG
Park
Young Shik
YS
D000595:Amino Acid Sequence; D000818:Animals; D002384:Catalysis; D004330:Drosophila / Q000201:enzymology; D004795:Enzyme Stability; D004926:Escherichia coli / Q000201:enzymology*; D006358:Hot Temperature; D006801:Humans; D007700:Kinetics; D008969:Molecular Sequence Data; D019761:Phosphorus-Oxygen Lyases / Q000235:genetics / Q000378:metabolism*; D011621:Pteridines / Q000378:metabolism*; D011622:Pterins / Q000378:metabolism*; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D013379:Substrate Specificity
D011621:Pteridines; D011622:Pterins; D011994:Recombinant Proteins; C025596:7,8-dihydropterin; C045652:dyspropterin; C016727:sepiapterin; D019761:Phosphorus-Oxygen Lyases; C043497:6-pyruvoyltetrahydropterin synthase; C465227:YgcM protein, E coli