164 UNITY AND DIVfeRSITY IN BIOCHEMISTRY 



every enzyme of this type has not been proved. In a number of cases, the 

 aerobic transhydrogenases are metalloproteins containing a metal (Fe, Cu 

 or Mo) in addition to the flavin nucleotide. 

 Here is a representative Ust of these enzymes : 



1. (with FMN) 



TPNH -^ Og-transhydrogenase (see "yellow enzyme"); 

 L-amino acids -^ Og-transhydrogenease (L-amino acid oxidase). 



2. (with FAD) 



Aldehyde -^ Og-transhydrogenase (aldehyde — oxidase) ; 

 Xanthine -^ Og-transhydrogenase (xanthine — oxidase). 



(c) Anaerobic Transelectronases 



Some enzymes of this type have a flavin prosthetic group, others a haem 

 prosthetic group. 



In the first category are the metalloflavoproteins (Fe) such as DPN- 

 cytochrome reductase and TPN-cytochrome reductase, enzymes which 

 Hoffmann-Ostenhof suggests should be called DPNH -^ cytochrome- 

 c-transelectronase and TPNH -^ cytochrome-c-transelectronase, 



respectively. 



Among the anaerobic transelectronases containing haem derivatives are 

 the cytochromes, described on page 119. 



{d) Aerobic Transelectronases 



Cytochrome oxidase or cytochrome-flg is an example of this type of 

 enzyme (see p. 120). It is highly specific for the transport of electrons from 

 cytochrome-c to oxygen. The phenolases (see p. 123) are also aerobic 

 transelectronases, transporting electrons from copper to oxygen. 



E. Hydroperoxidases 

 (See page 120). 



F. Lyases and Synthetases 



This name applies to enzymes catalysing reactions of the type 



A +B ^C 



whilst the enzymes of the preceding categories (A, B, C, D, E) catalysed 

 reactions of the type 



A +B ^C +D 



Among the lyases and synthetases, some break or form a C — C bond, 

 these are the carboxylases or carbosynthetases, whilst others split or form 

 C — N or C — S bonds. Among the lyases we have the hydrases and de- 

 hydrases, enzymes which add or remove water. 



