92 SUBCELLULAR PARTICLES 



tide requires relatively mild methods such as sonication or other devices for com- 

 minution. However, the degradation of subunits into the constituent protein com- 

 ponents is an entirely different kettle of fish. For this purpose physical methods are 

 valueless, and only chemical methods rather brutal in nature can do the trick. 

 Clearly the forces which hold repeating units together are entirely different from 

 the forces which bind together the components of any one repeating unit. 



Before we can consider in detail the various fragmentation products of the 

 electron transfer particle it would be appropriate to list the known components 

 of the electron transfer chain (table i). There are two flavoproteins^ — the succinic 

 and DPNH dehydrogenases. The flavin prosthetic group which is flavin adenine 

 dinucleotide is readily detached from the DPNH dehydrogenase by acid, but not 

 from the succinic dehydrogenase. Tryptic digestion is required for the release of 

 flavin from the succinic dehydrogenase. This difference in the extractability of the 

 flavins has made it possible to estimate accurately the amount of each flavoprotein 

 in a given particle. 



There are four known hemoproteins in the electron transfer particle of beef 

 heart mitochondria; viz., cytochromes a, b, c^, and c. They are readily distin- 

 guishable by spectroscopic and other properties, and they have vastly different 

 enzymatic properties, which is what would be expected in view of their different 

 positions and roles in the electron transfer chain. There are chemical as well as 

 spectroscopic methods of analysis available which make it possible to determine 

 the exact amount of any cytochrome in a given particle. 



The lipoproteins represent the third category of protein components of the 

 electron transfer chain. They are relatively new entities. The first to be isolated 

 and characterized as a definite entity we have called the Q lipoprotein (i). 

 It is too early to say exactly how many lipoproteins are present in the electron 

 transfer particle. At present three have been isolated: one associated with co- 

 enzyme Q, the second with cytochrome c^ and the third with the DPNH dehydro- 

 genase. 



The lipoproteins are complexes of lipid and protein which behave as bona fide 

 molecules. The Q lipoprotein we have recently described has about 96 per cent 

 lipid and 4 per cent protein. The ratio of lipid to protein will probably vary from 

 one lipoprotein to the next. 



Associated with the flavoproteins, hemoproteins and lipoproteins are certain 



Table i. Known components of electron transport particle 



Flavoproteins 



Succinic (£s) 



DPNH (fn) 

 Hemoproteins 



C\ tiKlironies a, h, c\, c 



Lipoproteins 



Q, ri-lipoprotein complex 

 Sni.ill molecules 



Coenzyme Q, carotenoids, a-tocopherol, fn 

 Metals 



Iron (non-heme), copper 



