Purification and properties of an extracellular esterase from a cold-adapted Pseudomonas mandelii

An extracellular esterase, EstK, was purified from the psychrotrophic bacterium Pseudomonas mandelii grown at 25°C. Prior to harvest, cells were treated with 0.2 M MgCl₂ to precipitate lipopolysaccharides in the outer membranes, which otherwise form aggregates with the secreted enzymes. EstK was purified to homogeneity using standard procedures. It had substrate specificity towards esters of short-chain fatty acids, particularly, p-nitrophenyl acetate. Optimum activity of EstK was at 40°C; at 4°C the activity was ~50% of its maximum. EstK has a unique substrate preference for p-nitrophenyl acetate and remains active at low temperatures.