Cross-link formation of phage lambda DNA in situ photochemically induced by the furocoumarin derivative angelicin.

The combined action of 365 nm ultraviolet light and xanthotoxin or angelicin inhibits the injection of phage lambda into the host. For both furocoumarin derivatives the inhibition of injection is discussed in terms of photochemically induced cross-linking of the DNA inside the phage heads; Cross-linking of DNA has previously been described for xanthotoxin (Musajo, L. and Rodighiero, G. (1972) in Photophysiology (Giese, A.C., ed.), Vol. VII, pp. 115-147, Academic Press, New York and Scott, B.R., Pathak, M.A. and Mohn, G.R. (1976) Mutation Res. 39, 30-74) but not for angelicin. The electronic structures in the first excited states calculated by means of quantum chemistry according to the Pariser-Parr-Pople method are very similar for xanthotoxin, psoralen and angelicin. Hence angelicin should be capable of acting bifunctionally like xanthotoxin, but for sterical reasons such reaction should be possible only for the folded DNA, as in phage heads, but not for diluted aqueous solution of DNA.