An octaethylene glycol monododecyl ether-based mixed micellar assay for determining the lipid acyl hydrolase activity of patatin |
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Authors: | Mercedes Jimenez Josefa Escribano Manuela Pérez-Gilabert Soledad Chazarra Juana Cabanes Francisco García-Carmona |
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Affiliation: | (1) Mercedes Jiménez Atiénzar, Departamento de Bioquímica y Biología Molecular A, Unidad Docente de Biología, Facultad de Veterinaria, Universidad de Murcia, Campus de Espinardo, 30071 Murcia, Spain |
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Abstract: | Patatin was extracted from potato tubers (Solanum tuberosum L. cv. Spunta) and purified to homogeneity by ammonium sulfate salt fractionation and one sole chromatographic step. A spectrophotometric mixed micellar assay for patatin lipid acyl hydrolase (LAH) activity was designed with the detergent octaethylene glycol monododecyl ether (C12E8). Patatin LAH used p-nitrophenyl butyrate (PNP-butyrate) as substrate when solubilized in (C12E8) micelles. In the mixed micellar system, patatin LAH responds to the PNP-butyrate surface concentration expressed as mol% (=[PNP-butyrate]·100/([detergent]-critical micellar concentration)) and not to the molarity of PNP-butyrate. The kinetic parameters were determinined; V max was independent of the mixed micelle concentration, as was K m, when expressed as mol%. However, K m was dependent on C12E8 concentration when expressed in molar concentration. C12E8/PNP-butyrate proved to be a reliable system for assaying patatin LAH activity and is superior to the commonly used Triton X-100 and SDS methods. It permits investigation of the substrate requirements of patatin LAH activity because the concentration-independent K m can be determined both in mol% and as the absolute number of substrate molecules per micelle. In addition, the detergent did not affect the enzyme activity. |
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