Structural modifications in biosynthetic melanins induced by metal ions

Palumbo, Anna; d’Ischia, Marco; Misuraca, Giovanna; Prota, Giuseppe; Schultz, Thomas M.

doi:10.1016/0304-4165(88)90166-3

Cited by 83 publications

(30 citation statements)

References 20 publications

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“…At somewhat lower pH the same concentrations will aggregate more rapidly to produce the brown/black pigment associated with melanin. Hence in addition to the ring closure of dopachrome favouring formation of DHICA rather than DHI [14], the effect of Cu 2+ ions is that they can bind to such anionic groups, disturb the stability, and cause the more rapid aggregation as we observe. In the absence of Cu 2+ ions at pH 9 dark melanin aggregates are present, but absent at pH 10 as borne out by the transparent (red/brown) solution observed.…”

Section: 2fluorescence Spectramentioning

confidence: 56%

“…Moreover, addition of metal ions, particularly Cu 2+ , has previously been found to accelerate the formation of eumelanin from L-DOPA. Cu 2+ has been suggested to bind predominantly to hydroxyl groups at pH 7-11 [13] and increase the concentration of DHICA in synthetic eumelanin formed from L-DOPA in the presence of tyrosinase by catalyzing the re-arrangement of the intermediate dopachrome in favour of DHICA rather than DHI [14].…”

Section: Introductionmentioning

confidence: 99%

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Metal ion influence on eumelanin fluorescence and structure

Sutter¹,

Birch²

2014

Methods Appl. Fluoresc.

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Melanin has long been thought to have an unworkably weak and complex fluorescence, but here we study its intrinsic fluorescence in order to demonstrate how metal ions can be used to control the rate of formation, constituents and structure of eumelanin formed from the well-known laboratory auto-oxidation of 3, 4-dihydroxy-L-phenylalanine (L-DOPA). The effect on eumelanin absorption and fluorescence of a range of solvated metal ions is reported including Cu, Zn, Ni, Na and K. Monovalent cations and Zn have little effect, but the effect of transition metal cations can be considerable. For example, at pH 10, copper ions are shown to accelerate the onset of eumelanin formation, but not the rate of formation once it commences, and simplify the usual complex structure and intrinsic fluorescence of eumelanin in a way that is consistent with an increased abundance of 5,5-dihydroxyindole-2-carboxylic acid (DHICA). The presence of a dominant 6 ns fluorescence decay time at 480 nm, when excited at 450 nm describes a distinct photophysically species, which we tentatively assign to small oligomers. Copper is well-known to normally quench fluorescence, but increasing amounts of copper surprisingly leads to an increase in the fluorescence decay time of eumelanin, while reducing the fluorescence intensity, suggesting copper modification of the excited state. Such results have bearing on diverse areas. The most accepted morphology for melanin is that of a graphite-like sheet structure, and one which readily binds metal ions, an interaction that is thought to have an important, though as yet unclear bearing on several areas of medicine including neurology. There is also increasing interest in bio-mimicry by preparing and labelling sheet structures with metal ions for new electronic and photonic materials.

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Section: 2fluorescence Spectramentioning

confidence: 56%

Section: Introductionmentioning

confidence: 99%

Metal ion influence on eumelanin fluorescence and structure

Sutter¹,

Birch²

2014

Methods Appl. Fluoresc.

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“…The amine and catechol hydroxyl groups of DHI and DHICA as well as the carboxylic group of DHICA can work as primary or secondary binding sites for metal cations [11,48] ; factors determining the binding site for each cation are mainly the type of eumelanin (natural or synthetic) and the pH (Table I). Crucial features of melanogenesis, such as the rate of formation of eumelanin [49] and the relative percentage of the two indolic building blocks present (DHI versus DHICA), [50,51] are influenced by the presence of metal ions. Whether their influence on self-assembly and structure is significant [52,53] or not [54] is still a matter of debate.…”

Section: Introductionmentioning

confidence: 99%

Natural melanin pigments and their interfaces with metal ions and oxides: emerging concepts and technologies

Mauro

Soliveri

et al. 2017

MRS Communications

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Melanin (from the Greek μέλας, mélas, black) is a biopigment ubiquitous in flora and fauna, featuring broadband optical absorption, hydration-dependent electrical response, ion-binding affinity as well as antioxidative and radical-scavenging properties. In the human body, photoprotection in the skin and ion flux regulation in the brain are some biofunctional roles played by melanin. Here we discuss the progress in melanin research that underpins emerging technologies in energy storage/conversion, ion separation/water treatment, sunscreens, and bioelectronics. The melanin research aims at developing approaches to explore natural materials, well beyond melanin, which might serve as a prototype benign material for sustainable technologies.

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“…These studies have mainly focused on nonenzymatic aspects of melanins such as cation exchange properties, structural modification by metal ions and rearrangement of dopachrome. 23,24 However, in the melanincontaining tissues there are high qualities of some heavy metals, in particular zinc, copper, and iron, 32 for example, high levels of such metal ions have been found in the choroids of eye, 33,34 black hair, 35 pigmented moles, 36 and human melanomas. 37 The binding of transition metals to the MT leads to the structural and functional changes as a consequence of such interactions.…”

Section: +mentioning

confidence: 99%

Non-Essential Activation of Co²⁺and Zn²⁺on Mushroom Tyrosinase: Kinetic and Structural Stability

Gheibi¹,

Saboury²,

Sarreshtehdari³

2011

Bulletin of the Korean Chemical Society

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Tyrosinase is a widespread enzyme with great promising capabilities. The Lineweaver-Burk plots of the catecholase reactions showed that the kinetics of mushroom tyrosinase (MT), activated by Co 2+ and Zn 2+ at different pHs (6, 7, 8 and 9) obeyed the non-essential activation mode. The binding of metal ions to the enzyme increases the maximum velocity of the enzyme due to an increase in the enzyme catalytic constant (k cat ). From the kinetic analysis, dissociation constants of the activator from the enzyme-metal ion complex (K a ) were obtained as 5 × 10 4 M −1 and 8.33 × 10 3 M −1 for Co 2+ and Zn 2+ at pH 9 and 6 respectively. The structural analysis of MT through circular dichroism (CD) and intensive fluorescence spectra revealed that the conformational stability of the enzyme in these pHs reaches its maximum value in the presence of each of the two metal ions.

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Structural modifications in biosynthetic melanins induced by metal ions

Cited by 83 publications

References 20 publications

Metal ion influence on eumelanin fluorescence and structure

Metal ion influence on eumelanin fluorescence and structure

Natural melanin pigments and their interfaces with metal ions and oxides: emerging concepts and technologies

Non-Essential Activation of Co²⁺and Zn²⁺on Mushroom Tyrosinase: Kinetic and Structural Stability

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Structural modifications in biosynthetic melanins induced by metal ions

Cited by 83 publications

References 20 publications

Metal ion influence on eumelanin fluorescence and structure

Metal ion influence on eumelanin fluorescence and structure

Natural melanin pigments and their interfaces with metal ions and oxides: emerging concepts and technologies

Non-Essential Activation of Co2+and Zn2+on Mushroom Tyrosinase: Kinetic and Structural Stability

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Non-Essential Activation of Co²⁺and Zn²⁺on Mushroom Tyrosinase: Kinetic and Structural Stability