IV. BIOCHEMICAL SYSTEMS 



339 



lyze to rihoHaviii phosphate ami adenylic acid. The absorption spectra 

 of riboflavin and flavin adenine diinideotide are f2;i\'en in Fi^-. 2.''' 



B. ENZYMES 



The classification of flavoproteins based upon their behavior during in 

 vitro experiments may lead to erroneous conclusions about their intracellu- 

 lar function. Relatively sHght changes in the method of isolation may pro- 

 duce fla\-oproteins with different properties and with sluggish activities not 

 normally associated with cellular action. Until more definitive information 

 becomes available, one should not discount the suspicion that an artifact 



230 



270 



310 



350 390 430 



Wavelength in m^ 



Fig. 2. Absorption spectra of riboflavin ( 



cleotide (-- ). (Warburg and Christian".) 



470 



510 



550 



-) and flavin adenine dinu- 



may have been produced in some of the isolation procedures. During the 

 development of our present knowledge of flavoproteins a system of nomen- 

 clature has evolved which binds specific proteins to specific substrates. 

 Whether or not such activities are as represented, it is necessary to charac- 

 terize the individual enzymes in this manner in order to appreciate not 

 only the work which has been done but also that which will be reported. 

 Table I summarizes the known flavoproteins and some of their charac- 

 teristics. 



1. Old Yellow Enzyme 



a. Preparation and Properties 



The discovery, isolation, and some of the properties of the yellow oxida- 

 tion enzyme have been discussed in the sections describing the coenzyme 

 riboflavin phosphate (see p. 337). 



