Photolability of bleomycin and its complexes.

Bleomycin has been found to be very sensitive to photolysis and on irradiation with the full spectral range of a medium-pressure mercury lamp undergoes a number of photo-induced reactions; there is a process in which the absorbance at 310 nm decreases, and a slower process in which it increases with photolysis time. The faster process can be studied by irradiation at approximately 300-350 nm, is complete in approximately 8 min, obeys first order kinetics, but is itself biphasic. The Fe(II) and Cu(II) complexes of bleomycin are also photolabile, as is the bleomycin-DNA complex.