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Physical state of inhibitor fatty acids and linoleate solutions under lipoxygenase assay conditions
Author(s) -
Gibian Morton J.,
Colanduoni John
Publication year - 1984
Publication title -
lipids
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.601
H-Index - 120
eISSN - 1558-9307
pISSN - 0024-4201
DOI - 10.1007/bf02534793
Subject(s) - chemistry , surface tension , lipoxygenase , substrate (aquarium) , micelle , fatty acid , chromatography , critical micelle concentration , kinetics , enzyme , organic chemistry , aqueous solution , thermodynamics , physics , oceanography , quantum mechanics , geology
A variety of fatty acids, which are potential competitive inhibitors of soybean lipoxygenase (EC 1.13.11.12), give kinetically unstable mixtures in standard assay solutions containing linoleate (substrate). In the assay solution (pH 10, 0.1 M borate, 1.63% ethanol), each fatty acid by itself shows normal surface tension vs concentration behavior; but, despite a range of solubilization techniques in the presence of 10 μM or higher linoleate and low concentrations of these materials, irreproducible surface‐tension readings and inhibition kinetics results. This inhomogeneity (or kinetic instability) disappears as the concentration increases. Critical micelle concentration (CMC) values of mixtures are not additive, and binary mixture behavior depends on fatty acid structure. Several lines of observation, including CMC values and actual surface tension (γ) values for several systems, suggest premicellar heterodimer or higher mixed aggregate formation. Lipids with K i significantly above the irreproducible surface‐tension range give good kinetic behavior, and K i is reported. The results are in accord with earlier work on aspects of these systems. Complementary solution physical studies must be done for any kinetic (or specificity) determinations of enzymes using lipids.