Fluorimetric Assay of the Activity of Extracellular Lipases of Pseudomonas fluorescens and Serratia marcescens

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Abstract
A fluorimetric assay was carried out on the activity of extracellular lipase concentrations obtained from Serratia marcescens and Pseudomonas fluorescens using as substrates fatty acyl esters of 4‐methylumbelliferone (4‐methylumbelliferone elaidate, 4‐methylumbelliferone nonanoate, 4‐methylumbelliferone butyrate, 4‐methylumbelliferone palmitate and 4‐methylumbelliferone oleate) at pH 4.0, 6.0, 8.0 and 10.0. The Ser. marcescens and Ps. fluorescens were cultured in Pope and Skerman's basal medium (Skerman 1957) supplemented with 0.5% (w/v) of a commercial medium. The extracellular lipases were isolated and purified by ammonium sulphate precipitation. The assay was carried out by relating the fluorescent intensity emitted by two lipase concentrations on five substrates against four standard curves. These standard curves were prepared by estimating the intensity of fluorescence given by varying dilutions of 4‐methylumbelliferone at the four pH levels. The results indicated that the oleic ester of 4‐methylumbelliferone was a suitable substrate at pH 8.0 and pH 10.0. These pH values were also optimum for fluorescent intensity on substrates of 4‐methylumbelliferone elaidate, 4‐methylumbelliferone butyrate and 4‐methylumbelliferone palmitate. However, on substrate 4‐methylumbelliferone nonanoate, the optimum pH was 4.0.