RECONVERSION OF SULFHEMOGLOBIN 495 



dominantly choleglobin, not sulfhemoglobin, the formation of the 

 hemoglobin-hydrogen peroxide complex from oxyhemoglobin and 

 hydrogen donors such as phenylhydroxylamine and phenylhydrazine 

 catalyzes not only the formation of choleglobin but also that of 

 sulfhemoglobin, in vivo as well as in vitro (80,4.54,1010, 139Jf.,1^39, 1945, 

 1946,2264,2587). Lemberg and co-workers {1701) have shown that 

 phenylhydrazine in vitro initially accelerates the formation of sulf- 

 hemoglobin, while at a later stage of the reaction more choleglobin 

 is formed. In these reactions the hydrogen donor probably takes 

 over the role of the XH2 group in globin : 



HbCXHOO, + HoA -> Hb(XH.) • H0O2 + A 

 HbfXH,) • H,0., + HoS -^ HbCXHOS + 2 H.O 



7.6. Reconversion of Sulfhemoglobin to Protoporphyrin 

 Derivatives and Nature of Its Prosthetic Group 



In spite of earlier claims to the contrary {454), it has later been 

 shown that sulfhemoglobin cannot be reconverted to hemoglobin. 

 Nijveld {2054) has recently claimed a conversion by cyanide and 

 ferricyanide into hemiglobin cyanide, accompanied by removal of 

 the extra sulfur atom. The identity of the resulting compound with 

 hemiglobin cyanide has, however, not been proven. 



It is certain, on the other hand, that by alkali or pyridine denatur- 

 ation sulfhemoglobin is transformed into protohemochromes {628, 

 1701,1945), in spite of claims to the contrary by Barkan and Schales 

 {164) which were based on the study of products consisting mainly 

 of choleglobin. The band in the orange part of the spectrum disap- 

 pears and the visible band of protohemochrome and the Soret band 

 reappear in original strength; carboxysulfhemoglobin has only a weak 

 absorption at 415 m^. The transformation by pyridine or hydrazine 

 is not extremely rapid. Apparently unstable sulfhemochromes are 

 first formed; with pyridine a band at 612 mju was observed (carboxy 

 compound, 624 ni/u), with hydrazine, at 610 m/i (carboxy compound, 

 618 m/x). These are then more slowly transformed into protohemo- 

 chromes {1527). 



Protoporphyrin has been obtained from sulfhemoglobin solutions 

 by List {1783), but only Nijveld {2054) has proven that it is derived 

 from sulfhemoglobin, and not from the splitting by acid of accom- 

 panying hemoglobin. 



Haurowitz (lloGJ 170) obtained a sulfur-containing porphyrin from 

 sulfhemoglobin. In spite of the fact that in his second study Haurowitz 



