A.1. Photoresponsive biomolecules
Intensely colored visible-light absorbing molecules are an
essential part of our living environment. A quite small number
of chromophore types and photoactive pigments seems to be
sufficient to deal with the basic photobiological responses and
light-dependent functions that have evolved in natural systems.
Prominent representatives of organic chromophore molecules in
this context (Fig. 3) are the flavins, pterin derivatives such as
MTHF 2 , porphyrins and related tetrapyrrole pigments 3 , car-
otenoids 4 , or conjugated oxidation products of amino acids such
as the chromophores of the green fluorescent proteins 5 ( 22 – 24 ).
There are also many building blocks and redox cofactors pres-
ent in biological systems including purines, quinones, coenzymes
such as NADH, and other organic chromophores displaying
FIG. 3. Examples of natural photoantenna chromophores: ( 2 ) 5,10-
methenyltetrahydrofolate (MTHF), a blue light photoreceptor pigment
present in photolyase and some cryptochromes; ( 3 ) Pheophytina, the
primary electron acceptor in cyanobacterial oxygenic photosynthesis.
( 4 ) 11-cis-retinal, which is involved as sensory photoreceptor compo-
nent in the opsin-based visual process of animals; and ( 5 ) the p-
hydroxy-benzylidene-imidazolinone chromophore (HBDI) of the green
fluorescent protein from bioluminescent marine species.
240 GÜNTHER KNÖR AND UWE MONKOWIUS