ENZYMES 163 



(c) Anaerobic transelectronases 



R + R'+ ^ R+ + R' 



e.g. DPNH -> cytochrome-t-transelectronase or DPN-cytochrome- 

 reductase. 



(d) Aerobic transelectronases 



R + O2 ^ R+ + Or 

 e.g. Cytochrome oxidase or cytochrome-^g. 



(a) Anaerobic Transhydrogenases 

 1. Enzymes Specific for the Pyridine Nucleotides 

 The reaction which is catalysed is : 



DPN (or TPN) + RHo^ DPNH (or TPNH) + R 

 or more correctly 



DPN+ (or TPN+) + RHg^ DPNH (or TPNH) + R + H+ 



Here are a few examples of reactions catalysed by specific anaerobic 

 transhydrogenases 



a-glycerophosphate 



glycerol 



glucose 



lactic acid 



ethanol 



glucose-6-phosphate 

 2 SH-glutathione 



+ DPN+ ^ DPNH 



+ 

 phosphodihydroxyacetone 

 glyceraldehyde 

 gluconic acid 

 pyruvic acid 

 acetaldehyde 



+ TPN+ ^ TPNH 



+ 

 6-phosphogluconic acid 

 glutathione-S-S-glutathione 



2. Enzymes of Still Undefined Specificity 



The nature of the specific acceptor is unknown for choline-dehydro- 

 genase, thiamine-dehydrogenase, and succinic dehydrogenase which is a 

 metalloflavoprotein containing iron. 



{b) Aerobic Transhydrogenases 



The transfer of hydrogen takes place, in the presence of these enzymes, 

 to oxygen forming HgOa- The majority of these enzymes contain a flavin 

 prosthetic group (FMN or FAD), but the presence of this grouping in 



