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KINETICS OF SOYBEAN LIPOXYGENASES ARE RELATED TO pH, SUBSTRATE AVAILABILITY AND EXTRACTION PROCEDURES
Author(s) -
CHEDEA VERONICA S.,
VICAŞ SIMONA,
SOCACIU CARMEN
Publication year - 2008
Publication title -
journal of food biochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.507
H-Index - 47
eISSN - 1745-4514
pISSN - 0145-8884
DOI - 10.1111/j.1745-4514.2008.00169.x
Subject(s) - substrate (aquarium) , chemistry , lipoxygenase , enzyme , enzyme assay , chromatography , specific activity , biochemistry , defatting , isozyme , extraction (chemistry) , biology , ecology
ABSTRACT The kinetic patterns of pure soy lipoxygenase LOX‐1 and crude or defatted soybean extracts containing LOX isoenzymes (LOX‐1, LOX‐2 and LOX‐3) were studied by UV spectrometry at 234 and 280 nm, depending on their extraction and measurement conditions. Different pHs (from 6.0 to 9.0), corresponding to specific activation of LOX isoenzymes and the ratios of enzyme protein per substrate were used in order to evaluate the enzyme rates, as indicators of its affinity for substrate in different environments. The crude soy extract contained mainly LOX‐1 activity (measured at 234 nm, at pH 9.0) and LOX‐3, in an approximate ratio of 3:1. The LOX‐2 activity was very low. The defatted extracts buffered at pH 6.8 and 7.1 showed a low LOX‐1 and LOX 2 activity, but mostly LOX‐3 activity (measured at 280 nm, at pH 7.1), with a mirror‐type relation between the enzyme/substrate ratio and their enzymatic specific activity. The results suggest that defatting inhibits specifically the LOX‐1 activity and indicate the possibility to modulate LOX activity by modifications of enzyme/substrate ratios and modifications of pH in the enzyme environment.PRACTICAL APPLICATIONS Because of the specific kinetic behaviors of the three different LOXs found in crude soy extracts involved in off‐flavor generation, one can modulate the inhibition of these isoenzymes during soybean processing. Our experiments showed that pH variation could be a simple solution to inhibit the LOX isoenzymes, and therefore, the off‐flavor generation. From the analytical point of view, the techniques described in this article are designed to be as simple as possible, and easy to use at large‐scale level in food industry (food chain control). The idea is to minimize the number of separate chemical manipulations and, thereby, minimize errors. These studies can offer the background of further inhibition experiments in vitro using natural extracts. The LOX inhibition by natural antioxidants is related as well to pH and other factors influencing the enzyme's activity; this idea can be also valorized practically in the future.