Comparative Biochemistry of the Phenolase Complex

Hs, Mason

doi:10.1002/9780470122617.ch3

Cited by 158 publications

(35 citation statements)

References 355 publications

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“…Tyrosinase (E.C. 1.14.18.1) is a copper-containing oxidase which exhibits two unusual properties: (1) The enzyme is able to catalyse both the oxidation of monohydric phenols (cresolase activity), which involves oxygen insertion into the ring Pomerantz 1966), and the oxidation of dihydric phenols (catecholase activity), to generate the corresponding ortho-quinone products (Mason 1955); (2) Tyrosinase exhibits suicide-inactivation during the oxidation of catechols (Asimov & Dawson 1950;Seiji et al 1978;Tomita et al 1980;García-Cánovas et al 1987;Tudela et al 1988). …”

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confidence: 99%

Evidence Consistent with the Requirement of Cresolase Activity for Suicide Inactivation of Tyrosinase

Land

Ramsden

Riley

et al. 2008

Tohoku J. Exp. Med.

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Tyrosinase is a mono-oxygenase with a dinuclear copper catalytic center which is able to catalyze both the ortho-hydroxylation of monophenols (cresolase activity) and the oxidation of catechols (catecholase activity) yielding ortho-quinone products. Tyrosinases appear to have arisen early in evolution and are widespread in living organisms where they are involved in several processes, including antibiosis, adhesion of molluscs, the hardening of the exoskeleton of insects, and pigmentation. Tyrosinase is the principal enzyme of melanin formation in vertebrates and is of clinical interest because of the possible utilization of its activity for targeted treatment of malignant melanoma. Tyrosinase is characterised by an irreversible inactivation that occurs during the oxidation of catechols. In a recent publication we proposed a mechanism to account for this feature based on the orthohydroxylation of catecholic substrates, during which process Cu(II) is reduced to Cu(0) which no longer binds to the enzyme and is eliminated (reductive elimination). Since this process is dependent on cresolase activity of tyrosinase, a strong prediction of the proposed inactivation mechanism is that it will not be exhibited by enzymes lacking cresolase activity. We show that the catechol oxidase readily extracted from bananas (Musa cavendishii) is devoid of cresolase activity and that the kinetics of catechol oxidation do not exhibit inactivation. We also show that a species with the molecular mass of the putative cresolase oxidation product is formed during tyrosinase oxidation of 4-methylcatechol. The results presented are entirely consistent with our proposed mechanism to account for suicide-inactivation of tyrosinase.

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confidence: 99%

Evidence Consistent with the Requirement of Cresolase Activity for Suicide Inactivation of Tyrosinase

Land

Ramsden

Riley

et al. 2008

Tohoku J. Exp. Med.

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“…It is clear, therefore, that, during the oxidation of the substrate, a process occurs that catechol substrate as a cresol, i.e. a "cresolase" presentation as opposed to a "catecholase" presentation (Mason 1955). This leads to the catechol being oxidised to form a product able to undergo deprotonation and reductive elimination of an ortho-quinone which results in inactivation of the enzyme by formation of copper(0) at the active site.…”

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The Mechanism of Suicide-Inactivation of Tyrosinase: A Substrate Structure Investigation

Land

Ramsden

Riley

2007

Tohoku J. Exp. Med.

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. The Mechanism of Suicide-Inactivation of Tyrosinase: A Substrate Structure Investigation. Tohoku J. Exp. Med., 2007, 212 (4), [341][342][343][344][345][346][347][348] Tyrosinase is a copper-containing mono-oxygenase, widely distributed in nature, able to catalyze the oxidation of both phenols and catechols to the corresponding ortho-quinones. Tyrosinase is characterised by a hitherto unexplained irreversible inactivation which occurs during the oxidation of catechols. Although the corresponding catechols are formed during tyrosinase oxidation of monophenols, inactivation in the presence of monophenolic substrates is minimal. Previous studies have established the kinetic features of the inactivation reaction which is first-order in respect of the enzyme concentration. The inactivation reaction exhibits the same pH-profile and saturation properties as the oxidation reaction, classing the process as a mechanism-based suicide inactivation. The recent elucidation of the crystallographic structure of tyrosinase has stimulated a new approach to this long-standing enigma. Here we report the results of an investigation of the tyrosinase-catalysed oxidation of a range of hydroxybenzenes which establish the structural requirements associated with inactivation. We present evidence for an inactivation mechanism based on catechol hydroxylation, with loss of one of the copper atoms at the active site. The inactivation mechanism involves two linked processes occurring in situ: (a) catechol presentation resulting in α -oxidation, and (b) deprotonation of an adjacent group. On the basis of our experimental data we believe that a similar mechanism may account for the inhibitory action of resorcinols.tyrosinase; suicideinactivation; catecholase; cresolase; α -oxidation; deprotonation © 2007 Tohoku University Medical Press When catechols are oxidised by tyrosinase there is a consistent anomaly in the oxygen stoichiometry. This phenomenon is amplified as the enzyme concentration is reduced. At low enzyme concentration the reaction ceases before either the substrate or the oxygen are depleted and further substrate supplementation or re-oxygenation have no effect. However, further enzyme addition re-initiates the reaction and the extent of further oxidation is a linear function of the amount of enzyme added. The effect is not due to a nonspecific influence of protein addition and re-initiation of oxidation is not observed when heat-inactivated tyrosinase is added to the reaction mixture. It is clear, therefore, that, during the oxidation of the substrate, a process occurs that

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“…PPO1 and PPO2 are primarily expressed in crystal cells while PPO3 is mainly expressed in lamellocytes when Drosophila melanogaster was infected by parasite [12][13][14]. Nine PPO genes have been identified in Anopheles gambiae [15,16] while ten and three genes in Aedes aegypti and Culex quinquefasciatus, respectively [17]. In the honey bee Apis mellifera, the PPO cDNA was characterized [18].…”

Section: Introductionmentioning

confidence: 99%

Characterization of Prophenoloxidase in Resisting Adverse Stresses in Apis cerana cerana

Liu¹,

Yao²

2015

J Environ Anal Chem

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Comparative Biochemistry of the Phenolase Complex

Cited by 158 publications

References 355 publications

Evidence Consistent with the Requirement of Cresolase Activity for Suicide Inactivation of Tyrosinase

Evidence Consistent with the Requirement of Cresolase Activity for Suicide Inactivation of Tyrosinase

The Mechanism of Suicide-Inactivation of Tyrosinase: A Substrate Structure Investigation

Characterization of Prophenoloxidase in Resisting Adverse Stresses in Apis cerana cerana

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