SOME COMMENTS ON FLAVIN AND FLAVOPROTEIN 

 COMPLEXES AND SEMIQUINONES* 



Helmut Beinert 



Institute for Enzyme Research 



University of Wisconsin 



Madison, Wisconsin 



Interaction of Light with Flavins 



The flavins belong to the most "colorful" of the coenzymes — whether 

 we use this word in its true sense or in a metaphoric one. Not only 

 do they appear in forms of almost all colors of the spectrum, but they 

 also undergo a variety of reactions and are involved in a great num- 

 ber of biological processes. The light energy absorbed by flavins is 

 dissipated in various ways: Flavins may fluoresce or phosphoresce 

 under proper conditions, they may be photolysed, photoreduced, or 

 may act as photosensitizers of other compounds. Their chemilimiines- 

 cence has also been observed. 



Although these light reactions of flavins appear to be particularly 

 germane to the main topic of this symposium, I shall refrain from 

 discussing them here, as I have not made any contribution to this 

 subject myself and also very recently have reviewed this topic else- 

 where (2) . Furthermore, it is not clear whether the light reactions 

 of the flavin compounds are of major biological significance per se, 

 or whether they are merely an expression of the great reactivity 

 of this class of compounds. 



I would therefore like to extend here Dr. Velick's discussion on the 

 observation of excited states of coenzymes as a means of recognizing 

 their state, their environment, or structure. I shall summarize some 

 recent work on various forms of flavins and flavoproteins which can 

 be studied by their specific light absorption. Although our knowledge 

 in this area rests on purely empirical groimd thus far, it appears that 

 a rational approach to the interpretation of the spectra and spectral 

 peculiarities of flavins may not be in the too distant future (cf. 10) . 



•Recent experimental work of the author's laboratory, which is discussed here, 

 was supported by the National Institutes of Health (Grant A — 2512). 



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