518 PROTOPLASM 



The former is an iron porphyrin; its synthesis marks a great 

 advance in research on blood constitution. The formation of 

 hemoglobin is in a large measure dependent upon diet. A pure 

 milk diet produces anemia (in adult animals). A trace of iron 

 in the milk is not sufficient (hemoglobin contains iron), but a 

 trace of copper in addition to the iron will cure the anemia. 

 Studies on mammalian pigments, particularly in man, have been 

 limited mostly to those of the blood, but there are a number of 

 others of importance such as the bile pigment bilirubin and 

 numerous pigments occurring within cells, some of which are 

 hemin compounds. That hematin pigment which has come into 

 prominence of late, owing primarily to the work of Keilin, is 

 cytochrome. It is an intracellular respiratory enzyme, or pig- 

 ment, belonging to the iron porphyrin group, as does hemoglobin. 

 It was discovered by MacMunn (in 1886), and its existence now 

 confirmed by Keilin. Cytochrome is said to be of almost univer- 

 sal distribution (in all erobic but not in anerobic cells). 



Cytochrome proved to be more than just another pigment; 

 it brought together the opposing views of Wieland and Warburg 

 on respiration. The former had his hydrogen-transport theory 

 based on a model of platinum black, wherein oxygen plays no 

 part 



^H2 + Pt = A + PtHa 



{A being any oxidizable organic substance). From this point of 

 view, the catalysis is hydrogen activation: 



CHsC^-OH -^ CHsC/ + H2 



Warburg, too, had his model; it was of blood charcoal and capable 

 of oxidizing various substances, especially oxalic acid and amino 

 acids, in the presence of oxygen (see page 180 for a discussion of 

 this in reference to adsorption and narcosis). Warburg viewed 

 oxidation in tissues only from the point of view of oxygen activa- 

 tion, and he recognized but one enzyme (the Atmungsferment, now 

 known to be indophenol oxidase), while Wieland considered 

 oxidation only from the point of view of hydrogen transport but 

 thought that various specific agencies might be responsible. 



