other medical applications ( 34 ). Although the detailed
mechanisms causing such effects are not fully clear, it seems that
the cells directly involved in wound repair are affected upon irra-
diation. An overall acceleration of the electron transfer processes
in the respiratory chain could provide more ATP, which is neces-
sary for the wound-healing process. However, also some other
types of bioinorganic photoreactions may be of crucial relevance
in this context and have to be discussed ( 6 ). For example, the nit-
ric oxide generated in injured tissue is well known to inhibit the
catalytic center of cytochromecoxidase ( 35 ), and photoinduced
NO release can recover its function ( 36 ).
Another very interesting example of a photochemical reaction
directly involving the two chromophores 5 and 6 (Figs. 3 and 4)
has recently been described (37,38). The spectral changes of the
corresponding photoredox process are shown in Fig. 5.
Oxidative quenching of the photoexcited EGFP protein is not
only possible with cytochromecbut also achieved with a variety
of other electron acceptors, including biologically relevant ones
such as NADþor flavins( 37 ). Further, the photoinduced electron
transfer (PET) seems to favor a net two-electron process. It has
been observed both in solution and inside living organisms with-
out any special treatment. These findings give rise to
speculations that a possible biological function of green fluores-
cent proteins might be that of a light-activated electron donor
similar to the role of chlorophyll donating electrons to an accep-
tor in photosynthesis.
FIG. 4. Structures of cytc(PDB-code: 3CYT) andc-type heme ( 6 ).242 GÜNTHER KNÖR AND UWE MONKOWIUS