Inhibitory effect of coumarin derivatives on polyphenol oxidase activity

Cilj je ovog rada bio ispitati inhibicijski učinak 116 derivata kumarina iz skupina tiosemikarbazida, tiazolidinona, Schiffovih baza, čalkona, pirazolina te tiazolidindiona na aktivnost polifenol oksidaze. Rezultati ispitivanja su pokazali da 38 derivata kumarina inhibira aktivnost polifenol oksidaze, 26 nema učinak, a 52 izaziva prividno povećanje enzimske aktivnosti. Najučinkovitijim inhibitorima se pokazuju tiosemikarbazidi pokazujući ovisnost inhibicijskog učinka o supstituentu na položaju 4 tiosemikarbazidne skupine. Među ostalim potencijalnim inhibitorima ističe se 7 spojeva iz skupine tiazolidinona, 7 Schiffovih baza, 9 čalkona i pirazolina te 10 tiazolidindiona. Inhibicijski učinak derivata kumarina najvjerojatnije je uzrokovan ireverzibilnom inhibicijom zbog formiranja veze tiosemikarbazidne skupine s bakrom u aktivnom središtu enzima čime se sprječava pristup kisika te kompeticijskom inhibicijom zbog sličnosti aromatskog prstena u strukturi derivata sa supstratom L-DOPA. Prividno povišenje aktivnosti polifenol oksidaze može se pripisati prooksidativnom učinku derivata kumarina na supstrat polifenol oksidaze L-3,4-dihidroksifenilalanin i/ili djelovanju određenih derivata kumarina kao supstrata polifenol oksidaze. Prooksidativni učinak nekih tiazolidinona, pirazolina te tiazolidindiona na L-3,4- dihidroksifenilalanin je najvjerojatnije uzorkovan keto skupinama na tiazo i/ili kumarinskom prstenu. Derivati kumarina koji u svom sastavu sadrže 3,4-dihidroksifenilnu skupinu djeluju kao supstrati polifenol oksidaze.Inhibitory effect of 116 coumarin derivatives (thiosemicarbazides, thiazolidinones, Schiff bases, chalcones, pyrazolines and thiazolidindiones) on polyphenol oxidase activity was investigated. Thirty eight coumarin derivatives inhibited polyphenol oxidase, 26 derivatives showed no effect, and 52 caused apparent increase in enzyme activity. The most effective inhibitors were thiosemicarbazides showing the dependence of the inhibitory effect to the substituent at the position 4 of thiosemicarbazide chain. Among other potential inhibitors 7 thiazolidinones, 7 Schiff bases, 9 chalcones and pyrazolines and 10 thiazolidinediones were found to inhibit polyphenol oxidase. Inhibitory effect of coumarine derivatives was most likely due to interaction between thiosemicarbazide group and copper in the active site of enzyme preventing the access of molecular oxygen, as well as competitive inhibition due to the similarity of the aromatic ring in the coumarin derivatives structure with the substrate L-DOPA. The apparent increase in polyphenol oxidase activity could be attributed to the prooxidative effect of coumarin derivatives on the substrate of polyphenol oxidase L-3 4- dihydroxyphenylalanine and/or to the action of certain coumarin derivatives as polyphenol oxidase substrates. Prooxidative effect of some thiazolidinones, pyrazolins and thiazolidinediones on L-3,4- dihydroxyphenylalanine could be attributed to the oxidation potential of keto groups positioned on thiazo and/or coumarin ring. Coumarin derivatives containing 3,4-hidroxyphenyl group act as substrates of polyphenol oxidase