Many pesticides are being used in agriculture in order to increase the yield. Although the use of these chemicals cause a positive effect on crop production, certain pesticides, metabolites, and contaminants have created many unforeseen adverse effects on the environment. Pesticides may be present in very low concentrations, which may not cause immediate detectable effects. However, this small amount of chemicals can cause sub-lethal damage to organism and this is more insidious and difficult to define than acute toxicity. Many chemicals, especially pesticides, at relatively low dosages affect the metabolism of organisms by altering the activities of enzymes. Browning reactions occuring in food systems may be broadly classified into non-enzymatic and enzymatic reactions. Enzymatic browning is due to oxidation of phenolic compounds by the action of oxidoreductase enzymes. Enzymatic browning in fruits and vegetables can cause undesirable quality changes during handling, processing and storage. Moreover, this reaction significantly diminish consumer acceptance, storage life and value of the plant products. Therefore, browning is important when food is processed and preserved. The main enzyme responsible for the brownig reaction is polyphenol oxidase (PPO). Polyphenol oxidase is a bifunctional copper-containing oxidoreductase enzyme that uses molecular oxygen to catalyse one or both of the following reactions: the hydyroxylation of monophenols to o-diphenols (EC 1.14.18.1, monophenolase or cresolase activity) and the oxidation of o-diphenols to o-quinones (EC 1.10.3.2, diphenolase or catecholase activity). This study was conducted for purification and characterization of PPO from Nevsehir potato and to determine the in vitro effects of four commonly used pesticides namely (RS)-5-ethyl-2(4-isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl) nicotinic acid, propyl [3-(dimethylamino)propyl]carbamate hydrochloride, N-(phosphonomethyl)glycine, and 2,4-dichlorophenoxyacetic acid dimethylamine salt ?on PPO activity. PPO enzyme was obtained from Nevsehir potato with 15.16 % efficiency and 52.25 purification degree. Purified enzyme showed no activity against L-tyrosine and p-cresol, whereas it exhibited the maximum PPO activity against catechol, gallic acid, pyrogallol substrates. These results indicate that PPO enzyme in Nevsehir potato lacks in monophenolase (cresolase) activity and has only diphenolase (catecholase) activity. In optimum pH and temperature studies, catechol showed the maximum activity at pH 7.0 and 20 �C. KM and Vmax values for catechol substrate were determined as 5 mM and 5000 U/mL min, respectively. The inhibitory effects of the pesticides on PPO activity were determined by using the catechol as a substrate. IC50 values of the pesticides, causing up to 50 % inhibition of the enzymatic activity, were determined by means of activity percentage diagrams.The results revealed that all the pesticides inhibited the PPO enzyme activity in a concentration-dependent fashion.

Purification of polyphenol oxidase from Nevsehir potato (<i>Solanum tuberosum</i> L.) and investigation of its in vitro inhibition by some pesticides

248th National Meeting (2014)

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Purification of polyphenol oxidase from Nevsehir potato (Solanum tuberosum L.) and investigation of its in vitro inhibition by some pesticides