Inhibition Kinetics of Cabbage Butterfly (<Emphasis Type="Italic">Pieris rapae</Emphasis> L.) Larvae Phenoloxidase Activity by 3-Hydroxy-4-Methoxybenzaldehyde Thiosemicarbazone |
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Authors: | Chao-Bin Xue Wan-Chun Luo Lin Jiang Xian-Ye Xie Ting Xiao Lei Yan |
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Institution: | (1) College of Plant Protection, Key Laboratory of Pesticide Toxicology and Application Technique, Shandong Agricultural University, Shandong Tai’an, 271018, People’s Republic of China;(2) College of Chemistry and Material Science, Shandong Agricultural University, Shandong Tai’an, 271018, People’s Republic of China |
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Abstract: | Phenoloxidase (PO) is a key enzyme in insect development, responsible for catalyzing the hydroxylation of tyrosine into o-diphenols and the oxidation of o-diphenols into o-quinones. In the present study, the kinetic assay in air-saturated solutions and the kinetic behavior of PO from Pieris rapae (Lepidoptera) larvae in the oxidation of l-tyrosine (a monophenol) and l-DOPA (l-3, 4-dihydroxyphenylalanine) (a diphenol) was studied. The inhibitory effects of 3-hydroxy-4-methoxybenzaldehyde thiosemicarbazone
(3-H-4-MBT) on the monophenolase and diphenolase activities of PO were also studied. The results show that 3-H-4-MBT can inhibit
both the monophenolase and diphenolase activities of PO. The lag period of l-tyrosine oxidation catalyzed by the enzyme was obviously lengthened and the steady-state activities of the enzyme sharply
decreased. The inhibitor was found to be noncompetitively reversible with a K
I (K
I = K
IS) of 0.30 μmol/L and an estimated IC50 of 0.14 ± 0.02 μmol/L for monophenolase and 0.26 ± 0.04 μmol/L for diphenolase. In the time course of the oxidation of l-DOPA catalyzed by the enzyme in the presence of different concentrations of 3-H-4-MBT, the rate decreased with increasing
time until a straight line was approached. The microscopic rate constants for the reaction of 3-H-4-MBT with the enzyme were
determined. |
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Keywords: | Phenoloxidase Inhibition kinetics 3-hydroxy-4-methoxybenzaldehyde thiosemicarbazone Monophenolase Diphenolase Pieris rapae (L ) |
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