Sf. O'Handley et al., Orf135 from Escherichia coli is a nudix hydrolase specific for CTP, dCTP, and 5-methyl-dCTP, J BIOL CHEM, 276(8), 2001, pp. 5421-5426
Orf135 from Escherichia coli is a new member of the Nudix (nucleoside dipho
sphate linked to some other moiety, x) hydrolase family of enzymes with sub
strate specificity for CTP, dCTP, and 5-methyl-dCTP. The gene has been clon
ed for overexpression, and the protein has been overproduced, purified, and
characterized. Orf135 is most active on 5-methyl-dCTP (k(cat)/K-m = 301,00
0 m(-1) s(-1)), followed by CTP (k(cat)/K-m = 47,000 M-1 s(-1)) and dCTP (k
(cat)/K-m = 18,000 M-1 s(-1)). Unlike other nucleoside triphosphate pyropho
phohydrolases of the Nudix hydrolase family discovered thus far, Orf135 is
highly specific for pyrimidine (deoxy)nucleoside triphosphates. Like other
Nudix hydrolases, the enzyme cleaves its substrates to produce a nucleoside
monophosphate and inorganic pyrophosphate, has an alkaline pH optimum, and
requires a divalent metal cation for catalysis, with magnesium yielding op
timal activity. Because of the nature of its substrate specificity, Orf135
may play a role in pyrimidine biosynthesis, lipid biosynthesis, and in cont
rolling levels of 5-methyl-dCTP in the cell.