Kinetic properties of purified Pseudomonas aeruginosa phosphorylcholine phosphatase indicated that this enzyme may be utilized by the bacteria to colonize in different environments

Pseudomonas aeruginosa phosphorylcholine phosphatase from periplasmic extracts of bacteria grown on choline as the sole carbon and nitrogen source was purified to homogeneity. The enzyme represented nearly 1% of the total protein found in the periplasmic space and is a monomer of approximately 53 kDa with an isoelectric point of 7.5. The optimum pH with phosphorylcholine was in the range of 5-8; with phosphorylethanolamine there was a peak at pH 6, and with p-nitrophenyl-phosphate (p-NPP) the optimum was at pH 5. Studies carried out at pH 5 indicated: i) For the three substrates above, Mg2+, Zn2+, or Cu2+ was necessary for maximal activity. ii) With p-NPP, these cations bound to the free enzyme in an ordered bireactant system. iii) With phosphorylethanolamine, Mg2+, Zn2+, or Cu2+ bound to the free enzyme in an at random bireactant system. iv) With phosphorylcholine, maximal activity was obtained with cation concentrations as low as 100 nM. v) Al3+ ions were inhibitors of the enzyme activity. The n (Hill coefficient) values for the inhibition by Al3+ with phosphorylcholine or p-NPP were 1 or 4, respectively. vi) The enzyme exhibited two affinity sites for phosphorylcholine. With Mg2+, a site with a Km value of 0.5 mM was detected; the corresponding Vmax was 25 micromol min-1 (mg protein)-1; without Mg2+, the enzyme displayed Km and Vmax values of 0.09 mM and 4.2 micromol min-1 (mg protein)-1, respectively. Studies carried out at pH 7.4 indicated: i) The enzyme could not catalyze the hydrolysis of p-NPP, and phosphorylethanolamine was a poor substrate in either the presence or absence of divalent cations. ii) The enzyme activity measured with phosphorylcholine was independent of divalent cations or was not inhibited by Al3+ ions. iii) With or without Mg2+, the enzyme exhibited two affinity sites for phosphorylcholine; the Km values were 0.05 mM and 0.5 mM with their corresponding Vmax of 5.6 and 25 micromol min-1 (mg protein)-1, respectively.