Some kinetic properties of polyphenol oxidase obtained from dill (Anethum graveolens)

Abstract

Polyphenol oxidase (PPO) was partially purified from dill by (NH 4 ) 2 SO 4 precipitation followed by dialysis and gel filtration chromatography. Polyphenol oxidase activity was measured spectrophotometrically at 420 nm using catechol, dopamine and chlorogenic acid as substrates. Optimum pH, temperature, and ionic strength were determined with three substrates. The best substrate of dill PPO was found to be chlorogenic acid. Some kinetic properties of the enzyme such as V max, K M and V max /K M were determined for all three substrates. The effects of various inhibitors on the reaction catalysed by the enzyme were tested and I 50 values calculated. The most effective inhibitor was L-cysteine. Activation energies, E a , were determined from the Arrhenius equation. In addition, activation enthalpy, DH a , and Q 10 values of the enzyme were also calculated.

Kinetic Studies of Polyphenol Oxidase from White Yam (Dioscorea rotundata Poir) Tuber

“…In practice, the relative enzyme yield and purity depends on the cultivar and origin of the plant material in conjunction with the techniques of extraction protocol. Generally, the kinetic properties of PPOs have been reported in previous studies of several plant tissues, [16,22,[33][34][35][36] which, by and large, measured up with the present observed kinetic indices of DR-PPO. Notwithstanding, the Km value of DR-PPO (Km=13.70 mM) in the presence of the experimental substrate (catechol) was comparatively higher than to those of Jerusalem artichoke (Helianthus tuberosus) PPO: Km=5.09 mM, [33] apple (Malus pumila) PPO, using 4-methyl catechol and pyrogallol substrates: Km=2.24 mM and 8.04 mM, respectively [16].…”

“…Studies by Robert et al, [43] gave the inhibition constants of the following inhibitors of palmito (Acanthophoenix rubra) PPO to be: benzoic acid; Ki=0.14 mM, cinnamic acid; Ki=0.019 mM and sorbic acid Ki=0.15 mM. By comparative analyses, the experimental derived Ki=0.539 mM of PPO extracted from D. rotundata at [L-cysteine]=4.0 mM, was an indication that L-cysteine could serve as an effective inhibitor against enzymatic browning reactions in D. rotundata tuber as represented by previous studies of PPO inhibition kinetics of other plant genera [10,12,34,40,[44][45][46]. In synergy with the direct inhibitory actions on PPO activity, L-cysteine by virtue of its sulphydryl group, which is a strong nucleophile, forms colourless addition o-quinones derivatives or/and facilitates the reduction of quinones back to their corresponding phenol substrates [7,10,47].…”

“…The outcome of the extraction and purification protocol of DR-PPO (Table 1) measured up with those described elsewhere, [33,34] exemplified with the relatively satisfactory enzyme yield and purification fold of the final extract cocktail (Table 1). In practice, the relative enzyme yield and purity depends on the cultivar and origin of the plant material in conjunction with the techniques of extraction protocol.…”

How interactions between microbial resource demands, soil organic matter stoichiometry, and substrate reactivity determine the direction and magnitude of soil respiratory responses to warming

“…Basic chemical principles inform us that bond energies are substantially higher for the double C=C bonds (612 kJ mol À1 ) in pyrimidine than for the single C-C bonds of chitin (347 kJ mol À1 ; Weast, 1983;Masterston et al, 1985), and thus these two substrates effectively capture important functional differences among SOM compounds. Indeed, published values of E a of decay for isolated enzyme-substrate pairings, at optimal pH and temperature, suggest that aromatic rings require greater energy to decay: the aromatic compounds catechol and dopamine, when paired with polyphenol oxidase, exhibit E a of decay of approximately 14 and 12 kJ mol À1 , respectively (Sakiroglu et al, 2008). E a of decay of the more simply structured aldouronic acids are approximately half these values (6 kJ mol À1 ) when paired with a-D-glucuronidase (Mierzwa et al, 2005).…”

Kinetic Characterization of Tyrosinase-catalyzed Oxidation of Four Polyphenols

“…Chlorogenic acid has been reported as a substrate of polyphenol oxidase derived from apple [7] and dill (Anethum graveolens) [31] . The dill-derived polyphenol oxidase exhibited better affinity to chlorogenic acid than catechol and dopamine [31] . However, very little attention has been devoted to polyphenol oxidase mediated oxidation of the isomers of chlorogenic acid such as cryptochlorogenic acid and neochlorogenic acid.…”