Abstract:Barley grains of Ganpi 4 were selected as the research object to determine the parameters of UV spectrophotometry for the lipoxygenase (LOX-1) activity measurement. The effects of substrate concentration, extraction buffer pH, buffer pH of reaction system, extraction time and the ratio between extraction and substrate addition on LOX-1 activity measured by UV spectrophotometry were studied. The results indicated that LOX-1 activity increased at first, and then decreased with the substrate concentration increasing, and the peak activity appeared at 0.30 mmol·L-1 of substrate concentration, which was significantly higher than that of the other treatments; with the increasing of extraction buffer pH, the LOX-1 activity varied with two peaks and the enzyme activity reached 9.85 U·g-1 at pH 5.0, which was significantly higher than that of the other treatments; LOX-1 activity which was extracted for 30min was significantly higher than that of the other treatments, and the enzyme activity had the trend of decrease at the extraction time which above or below 30min; when the extraction addition was 50 μL and other conditions remained unchanged, LOX-1 activity increased at first, and then decreased as the substrate addition increased, and the enzyme activity with the substrate addition of 200 μL was significantly higher than that the other treatments. Finally, the parameters of UV spectrophotometry were determined: 30 minutes extraction time, 0.25 mmol·L-1 substrate concentration, pH 5.0 acetate extraction buffer, pH 6.4 phosphate reaction system buffer, and 1∶4 as the ratio between extraction and substrate addition. The results can be used as the reference for the determination of LOX-1 activity in barley grain by UV spectrophotometry.