Oxygenation and Oxidation 



a close approximation of the oxygen dissociation curve of the arterial 

 blood of man in vivo. 



CYTOCHROME C AND METABOLISM 



Without haemoglobin life would not be as we know it. The same may 

 be said for cytochrome c, functioning in the other phase of oxygen 

 homeostasis. Indeed, without the cytochrome system, haemoglobin 

 function would be an extravagance. 



The flexibility of the spectrophotometric technique is well illustrated 

 by its extension to such diverse measurements as those upon the very 

 concentrated solutions of haemoglobin or whole undiluted blood with 

 the 0-007 cm cuvette, discussed above, and the direct spectrophoto- 

 metric determination of cytochrome c, isolated in micro quantities 

 from small amounts of tissue, as individual rat organs. For the latter 

 purpose we have developed an isolation procedure and designed a 

 capillary cuvette-diaphragm technique 9 . The latter is shown diagram- 

 matically in Figure 6. The small volume needed to fill this cuvette 

 permits more concentrated extracts to be measured, while small 

 volume and long depth of layer cooperate to increase sensitivity. 



With these means, combined with partial hepatectomy, adapted as 

 a metabolic procedure 40 , we have undertaken a systematic investigation 

 of cytochrome c metabolism. The influence of such factors as diet 

 (high and no protein) 41 , anoxia, and parenteral cytochrome c adminis- 

 tration 42 were studied. This work encouraged the conclusion that 

 ' certain cellular components, like cytochrome c and PNA [ribose 

 nucleic acid], are preferentially produced or deposited in tissues, and 

 are important or essential in growth and proliferative processes, which 

 appear to depend on intrinsic (tissue) as well as extrinsic (dietary) 

 factors 41 .' 



Most recently I have turned to a study of hormonal influences, 

 particularly thyroxine, on cytochrome c. I was directed towards this 

 path by a number of suggestive observations 11 , which are summarized 

 in Tables II and ///. The concentration of cytochrome c in tissues was 

 proportional to their ' respiratory ' (oxidative) activity (Table II). In 

 a way this was curious, since actually cytochrome c is a substrate for 

 the enzyme, cytochrome oxidase. The concentrations of both substrate 

 and enzyme therefore have a relationship of proportionality, or, what 

 seems more likely, the concentration of the substrate is a limiting 

 factor in the activity. The other observation was derived from our 

 accumulated data on the total concentrations, in the bodies of several 

 species, of the three chromoproteins, haemoglobin, myoglobin, and 

 cytochrome c (Table III). Total haemoglobin was strictly proportional 



47 



