CYTOCHROME b 359 



If respiration is inhibited by narcotics, the absorption band of reduced 

 cytochrome b remains visible, while those of cytochromes a and c disappear 

 (14.91,1493,194^3,2734). From this Tamiya and Ogura (2734) concluded that 

 cytochrome b is normally oxidized by cytochrome a, acting as carrier between 

 cytochrome c and cytochrome b; cytochrome a was assumed to react with 

 the narcotics. Cytochrome b is, however, kept reduced in the presence of 

 narcotics only by dehydrogenase systems, not by other reducing substances 

 such as ;>-phenylenediamine. Keilin and Hartree (1491,1493) interpreted 

 these results therefore by assuming that a complex between cytochrome b 

 and dehydrogenase is formed, and by the action of narcotics is made inacces- 

 sible to ferricytochrome c. The position of cytochrome c between cyto- 

 chromes a and b in the reaction chain is, indeed, in better agreement with 

 the oxidation-reduction potentials of the cytochromes (cf. Section 5.2.). 



In adrenal medulla Huszak (1377) has observed a cytochrome bi 

 (absorption band at 559 n\n) and a peroxidase with a broad indistinct 

 absorption band at 559-553 van which, unlike the cytochromes, 

 reacts with carbon monoxide (Chapter IX, Section 3.5.). 



Cytochrome 62. A water-soluble cytochrome b has been found in 

 purified yeast lactic acid dehydrogenase, which is quite different from 

 the lactic acid dehydrogenase of mammals; it has been called cyto- 

 chrome b2 (Bach and co-workers, 112,113; Haas and co-workers, 

 1077). Its absorption bands lie at 560.5 m^ and 530 m^, but its con- 

 centration in the yeast cell is too small for spectroscopic observation. 

 The Soret band lies at 420 m^ for the ferrous, at 410 m/x for the ferric 

 enzyme. 



Cytochrome b2 appears to be an integral part of the yeast lactic 

 acid dehydrogenase and does not contain a flavoprotein. With pyri- 

 dine it gives pyridine protohemochrome. The same result had been 

 found by Roche {2304.) for the cytochrome b of Actinia. It is likely 

 that the protohemin isolated by Fischer from various cells originated 

 from cytochrome b. 



Cytochrome b2 oxidizes lactate, but does not react with cytochrome 

 c (113). According to Haas and collaborators (1077) it is also reduced 

 by the hexose-6-phosphate dehydrogenase system, while Gale (978) 

 observed reduction by the formic acid dehydrogenase system in 

 Escherichia coli. These claims have not been confirmed by Bach and 

 co-workers. "Cytochrome b2" may be a mixture of cytochrome b2 

 and lactic dehydrogenase, or it may contain protoheme bound to 

 the dehydrogenase. 



If the latter is found to be correct, "cytochrome b" may be a 

 mixture of similar protoheme dehydrogenase compounds. The vari- 



