PRIMING REACTIONS 



209 



indicates that phosphorylations with formation of energy-rich bonds take 

 place in conjunction with the following links of the respiratory chain : 

 (1) between succinate and cytochrome-c ; (2) between cytochrome-c and 

 oxygen; (3) between DPN and cytochrome-c ; at this point two phos- 

 phorylations appear to occur. 



This is summarized in Slater's scheme reproduced in Fig. 47. 



substrate level 



substrat 

 I 



1 



DPNH., 



oxidized substrate 

 (E' between ' 

 and 0.45V.) 



DPN 



eye. -reductase 



FADH2 



Fe++ 



■ cytochromes • 



a 

 Fe-H- 



FAD 



Fe-^+ Fe++ + 



J L 



0.)2 



0.2J V. 



:\ 



Fe++ 



Fe+++ 



H,0 



[oT] 



0.0 +0.26 +0.8 



oxido-reduction potential scale 



i-—E; (voIm) 



h 



' AE equivalent to 1~P. 

 12 Kfoi 



Fig. 48 (Lehninger) — A type of respiratory chain with a scale of oxido-reduction potentials 



The sequence of the intermediates, in the case of the chain where 

 a-ketoglutaric acid is the model substrate (in Fig. 46) is represented with 

 the corresponding oxidation-reduction potentials in Fig. 48. 



V. MECHANISMS FOR THE BREAKDOWN OF AMINO ACIDS 



A. General Mechanisms 

 (a) Decarboxylation of Amino Acids 



In the presence of decarboxylases amino acids give COj and an amine 

 according to the general reaction : 



R R 



I I 



NH2— CH— COOH ^ NHo— CH2 -f CO2 



this is referred to as "decarboxylation". 



REFERENCES 



Lehninger, A. L. (1955). Oxidative phosphorylation. Harvey Lectures, 49, 176-215. 

 Slater, E. C. (1956). Respiratory chain phosphorylation. Proceedings of the 3^'^ 



International Congress of Biochemistry, Brussels 1955. Academic Press, New 



York, 264-277. 



