An erythromycin esterase (molecular mass 51 200 Da) was purified from Pseudomonas sp. GD100, which was isolated from a salmon hatchery sediment sample from Washington State. The pI of the protein was 4.5^4.8. The enzyme was inhibited by 1 mM mercuric acid, and had the substrate specificity for structurally related 14-membered macrolides, which decreased in the order of oleandomycin, erythromycin A and erythromycin A enol ether. The activity for erythromycin A varied with temperature, but the effect of pH was minimal at pH 6.0^9.0. The half-life of the enzyme was estimated to be 8.9 h at 35 ‡C and 0.23 h at 55 ‡C, and the activation energy of the catalytic reaction of erythromycin A was estimated at 16.2 kJ mol 31 . ß
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