Kinetic properties of light-dependent ascorbic acid oxidation by melanin

Randolph D. Glickman; Raymond Sowell; Kwok Wai Lam

doi:10.1016/0891-5849(93)90045-V

Kinetic properties of light-dependent ascorbic acid oxidation by melanin

Randolph D. Glickman, Raymond Sowell, Kwok Wai Lam

Ophthalmology

Research output: Contribution to journal › Article › peer-review

27 Scopus citations

Abstract

The kinetic properties of ascorbic acid oxidation by light-activated melanin granules demonstrate the presence of a specific reactive site on the melanin granule saturable by ascorbic acid. Increased light intensity increased the V_max and reduced the K_m of this reaction, indicating increased affinity of the active site for ascorbic acid. The kinetics of this reaction are not markedly changed in a reduced-oxygen environment. Ascorbic acid oxidation is competitively inhibited by isoascorbic acid, an epimer of ascorbic acid, while other tested reducing agents are inactive. The K_i for isoascorbic acid is 1 mM, about the same as the K_m of ascorbic acid.

Original language	English (US)
Pages (from-to)	453-457
Number of pages	5
Journal	Free Radical Biology and Medicine
Volume	15
Issue number	4
DOIs	https://doi.org/10.1016/0891-5849(93)90045-V
State	Published - Oct 1993

Keywords

Ascorbic acid
Free radicals
Isoascorbic acid
Kinetics
Light
Melanin

ASJC Scopus subject areas

Biochemistry
Physiology (medical)

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10.1016/0891-5849(93)90045-V

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title = "Kinetic properties of light-dependent ascorbic acid oxidation by melanin",

abstract = "The kinetic properties of ascorbic acid oxidation by light-activated melanin granules demonstrate the presence of a specific reactive site on the melanin granule saturable by ascorbic acid. Increased light intensity increased the Vmax and reduced the Km of this reaction, indicating increased affinity of the active site for ascorbic acid. The kinetics of this reaction are not markedly changed in a reduced-oxygen environment. Ascorbic acid oxidation is competitively inhibited by isoascorbic acid, an epimer of ascorbic acid, while other tested reducing agents are inactive. The Ki for isoascorbic acid is 1 mM, about the same as the Km of ascorbic acid.",

keywords = "Ascorbic acid, Free radicals, Isoascorbic acid, Kinetics, Light, Melanin",

author = "Glickman, {Randolph D.} and Raymond Sowell and Lam, {Kwok Wai}",

note = "Funding Information: Acknowledgements -- This study was supported in part by research grants from the Air Force Office of Scientific Research (AFOSR-91-0208), NIH (EY 08213), the San Antonio Area Foundation, and a development grant from Research to Prevent Blindness, Inc.",

year = "1993",

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T1 - Kinetic properties of light-dependent ascorbic acid oxidation by melanin

AU - Glickman, Randolph D.

AU - Sowell, Raymond

AU - Lam, Kwok Wai

N1 - Funding Information: Acknowledgements -- This study was supported in part by research grants from the Air Force Office of Scientific Research (AFOSR-91-0208), NIH (EY 08213), the San Antonio Area Foundation, and a development grant from Research to Prevent Blindness, Inc.

PY - 1993/10

Y1 - 1993/10

N2 - The kinetic properties of ascorbic acid oxidation by light-activated melanin granules demonstrate the presence of a specific reactive site on the melanin granule saturable by ascorbic acid. Increased light intensity increased the Vmax and reduced the Km of this reaction, indicating increased affinity of the active site for ascorbic acid. The kinetics of this reaction are not markedly changed in a reduced-oxygen environment. Ascorbic acid oxidation is competitively inhibited by isoascorbic acid, an epimer of ascorbic acid, while other tested reducing agents are inactive. The Ki for isoascorbic acid is 1 mM, about the same as the Km of ascorbic acid.

AB - The kinetic properties of ascorbic acid oxidation by light-activated melanin granules demonstrate the presence of a specific reactive site on the melanin granule saturable by ascorbic acid. Increased light intensity increased the Vmax and reduced the Km of this reaction, indicating increased affinity of the active site for ascorbic acid. The kinetics of this reaction are not markedly changed in a reduced-oxygen environment. Ascorbic acid oxidation is competitively inhibited by isoascorbic acid, an epimer of ascorbic acid, while other tested reducing agents are inactive. The Ki for isoascorbic acid is 1 mM, about the same as the Km of ascorbic acid.

KW - Ascorbic acid

KW - Free radicals

KW - Isoascorbic acid

KW - Kinetics

KW - Light

KW - Melanin

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