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Dear Kris Weber,
It is true that 8-methoxypsoralen will fluoresce when excited at 360
nm, however, you may also induce unwanted photochemistry. Linear psoralens
undergo an extremely fast photoreaction with DNA. The initial interaction
between DNA and psoralen is the noncovalent intercalation of the psoralen
into the DNA double helix. Irradiation of the complex with near UV light
induces covalent bond formation between the double bond of a pyrimidine
base (predominately thymine) and the olefin of either the furan (major
product) or lactone moieties in the psoralen. This monaddition is fast;
the rate constant for the reaction of psoralen with thymine is on the order
of (10E+8)/(Ms). Upon absorption of a second photon, the monoadduct can
either fluoresce or covalently crosslink the DNA by undergoing a second
reaction with the olefin of the lactone (provided there is an adjacent
pyrimidine base). This second reaction can take place within a
microsecond.
We are developing a High Speed Optical Chromosome Sorter
based on selective, irreversible photoinactivation of unwanted chromosomal
DNA. One system of photoinactivation that we are using is the photoadduct
formation between psoralen molecules and unwanted chromosomal DNA. We have
used this reaction to successfully photoinactivate unwanted GM130
chromosomes in a flow system. With psoralen and UV light, we have been
able to form sufficient lethal photoadducts to reduce cosmid cloning
efficiencies of chromosomal DNA to <5 % while maintaining the clonability
of unirradiated DNA.
In light of the above, you should be cautious when using
8-methoxypsoralen (or other psoralen derivatives) in a flow system designed
solely for analysis.
For further information on this photochemisty see the following:
(1) Hearst, J. E.; Isaacs, S. T.; Kanne, D.; Rapoport, H.;
Straub, K. Q. Rev. Biophys. 1984, 17, 1-44.
(2) Averbeck, D. Photochem. Photobiol. 1989, 50, 859-882.
(3) Song, P. S.; Tapely, K. J. Photochem. Photobiol. 1979, 29,
1177-1197.
(4) Yokabata, K. E.; Jordan, J. M.; Chapman, O.; Kreil, C.
Photochem. Photobiol. 1986, 43, 391-401.
(5) Bensasson, R. V.; Land, E. J.; Salet, C. Photochem.
Photobiol. 1978, 27, 273-280.
(6) Johnston, B. H.; Johnson, M. A.; Moore, C. B.; Hearst, J.
E. Science 1977, 197, 906-908.
(7) Johnston, B. H.; Kung, A. H.; Moore, B.; Hearst, J. E.
Biochemistry 1981, 20, 735-738.
Best Wishes,
Mary Roslaniec
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