Advertisement

Pulsed Irradiation Studies of Some Reactions of Melanin Precursors

  • J. N. Chacon
  • M. R. Chedekel
  • E. J. Land
  • T. G. Truscott
Conference paper
Part of the NATO ASI Series book series (volume 15)

Abstract

Psoralen compounds appear to increase skin pigmentation when used clinically to treat skin disorders such as vitiligo (leukoderma) and are also the subject of current investigation as possible additives to sun-protective preparations to augment the skin-tanning response. In the melanocytes the process of melanin synthesis is thought to occur via an initial oxidation step catalyzed by the enzyme tyrosinase. Craw et al1 demonstrated that the triplet excited state of 8-methoxypsoralen (8-MOP) was capable of initiating the oxidation of the melanin precursor dopa by an electron transfer process. In the present study laser flash photolysis has been used to assess whether a similar interaction occurs when 3-CPs is used in place of 8-MOP. The laser flash photolysis apparatus used has 2 been described previously. The frequency doubled line (347 nm) of a ruby laser was employed as the excitation source. 3-CPs saturated solutions were made in 0.10 M phosphate buffer (pH 8.90) and flushed with nitrogen. The quenching of the psoralen triplet state was carried out at two different dopa concentrations (2.64×10-4 and 8.62×10-4 M). In the course of this study the reaction rate constant for interaction of 8-MOP and dopa was evaluated in 0.10 M phosphate buffer (pH=6.94), the value of 1.55x109 M-1 s-1 obtained agreeing well with that reported by Craw et al (2±1×109 M-1s-1). The 3-CPs triplet state decayed by first 5-1 order kinetics with a rate constant of 8.0×105 s-1, this rate constant being 5-13 larger than that found by Craw et al (2×105 s-1)3. The discrepancy may be a result of ground state quenching, an effect previously reported for order dopaquinone decay after thiol addition.

Keywords

Triplet State Electron Transfer Process Triplet Excited State Pulse Radiolysis Melanin Synthesis 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

References

  1. 1.
    Craw M, Chedekel MR, Truscott TG, Land EJ (1984) The photochemical interaction between the triplet state of 8-methoxypsoralen and the melanin precursor L-3,4-dihydroxyphenylalanine. Photochem Photobiol 39: 155–159CrossRefGoogle Scholar
  2. 2.
    McVie J, Sinclair RS, Truscott TG (1978) Triplet states of copper and metal-free phthalocyanines. J.Chem Soc Faraday II 74: 1870–1879Google Scholar
  3. 3.
    Craw M, Bensasson RV, Ronfard-Haret JC, Sa e Melo MT, Truscott TG (1983) Some photophysical properties of 3-carbethoxypsoralen, 8- methoxypsoralen and 5-methoxypsoralen triplet states. Photochem Photobiol 37: 611–615CrossRefGoogle Scholar
  4. 4.
    Sa e Melo MT, Averbeck D, Bensasson RV, Land EJ, Salet C (1979) Some furocoumarins and analogs: comparison of triplet properties in solution with photobiological activities in yeast. Photochem Photobiol 30: 645–651CrossRefGoogle Scholar
  5. 5.
    Ronfard-Haret JC, Averbeck D, Bensasson RV, Bisagni E, Land EJ (1982) Some properties of the triplet excited state of the photonsensitising furocoumarin: 3-carbethoxypsoralen. Photochem Photobiol 35: 479–489CrossRefGoogle Scholar
  6. 6.
    Dubertret L, Averbeck B, Zajdela F, Basagni E, Tnoustacchi E, Touraine R, Latarjet R (1979) Photochemotherapy (PUVA) of psoriasis using 3-carbethoxypsoralen, a non-carcinogenic compound in mice. Br J Dermatol 101: 379–389CrossRefGoogle Scholar
  7. 7.
    Prota G (1970) In: Riley V (ed) Pigmentation: Its Genesis and Biologic Control. Appleton Century Crofts Ifleridith Corp., New York, p 615.Google Scholar
  8. 8.
    Thompson A, Land EJ, Chedekel MR, Subbarao KV, Truscott TG (1985) A pulse radiolysis investigation of the melanin precursors 3,4-dihydroxyphenylalanine (dopa) and the cysteinyldopas. Biochim Biophys Acta 843: 49–57CrossRefGoogle Scholar
  9. 9.
    Keene JP (1964) Pulse radiolysis apparatus, J Sci Instr 41: 493–496ADSCrossRefGoogle Scholar
  10. 10.
    Prakash C, Carraro C, Pathak A (1987) Involvement of reactive oxygen species in the oxidation of tyrosine and dopa to melanin and in skin tanning, Biochem Biophys Res Comm 142: 265–274CrossRefGoogle Scholar
  11. 11.
    Rodgers MAJ, Snowden PT (1982) Lifetime of 1O2 (1Δg) in liquid water as determined by time-resolved infrared luminescence measurements, J Amer Chem Soc 104: 5541–5543CrossRefGoogle Scholar

Copyright information

© Springer- Verlag Berlin Heidelberg 1988

Authors and Affiliations

  • J. N. Chacon
    • 1
  • M. R. Chedekel
    • 2
  • E. J. Land
    • 3
  • T. G. Truscott
    • 1
  1. 1.Department of ChemistryPaisley CollegePaisleyScotland, UK
  2. 2.The Johns Hopkins UniversityUSA
  3. 3.Paterson Institute for Cancer ResearchChristie HospitalManchesterEngland, UK

Personalised recommendations