| Summary: | Partially purified lipoxygenase (LOX) extracts were obtained from Fusarium oxysporum, Fusarium proliferalum, Saccharomyces cerevisiae and Chlorella pyrenoidosa by precipitation with ammonium sulfate. The enzymatic extracts from F. oxysporum and S. cerevisiae both exhibited two optimal activities at pH 8.0 and 10.0 while those from F. proliferatum and C. pyrenoidosa showed one optimal pH at 6.0 and 4.5, respectively. The enzymatic extract from F. proliferalum showed the highest LOX activity. The lowest LOX activity was exhibited in the C. pyrenoidosa extract. At pH 8.0, LOX activity from F. oxysporum and S. cerevisiae was inhibited by potassium cyanide (KCN), exhibiting a non-competitive inhibitory effect; however, at pH 10.0, KCN had relatively little effect on enzyme activity. In addition, KCN markedly inhibited LOX activity from C. pyrenoidosa. In contrast, the results showed that the enzymatic activity from F. proliferatum remained relatively stable at KCN concentrations as high as 60 mM. The addition of 5 MM sodium ethylenediaminetetraacetate was found to increase the enzymatic activity from F. oxysporum by 50.3 and 16.6% at pH 9.0 and 10.0, respectively, from F. proliferatum by 50%, and produced a noticeable eight-fold increase in the enzymatic activity from C. pyrenoidosa. Hydroquinone (HQ) resulted in a 2-fold increase in LOX activity from F. proliferalum whereas a competitive inhibitory effect on LOX activity from S. cerevisiae was observed at pH 8.0. The enzymes from the four sources demonstrated an overall preference towards linoleic acid, followed by linolenic acid. In addition, the enzymatic extract from F. proliferatum showed a strong preference towards the glycerol fatty acid esters. Linoleic acid was bioconverted into 9- and 13-hydroperoxides (HPODEs) by all four extracts; in addition, the LOX activity in the F. oxysporum extract produced the 10- and 12-HPODEs from linoleic acid while that of the C. pyrenoidosa extract produced only the 10-HPODE. T
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