MECHANISM OF FORMATION OF VERDOHEMOCHROMES 469 



complex has time to cause some intramolecular oxidation before it 

 dissociates and is destroyed by catalase. 



If the primary compound of hemochrome with oxygen is to react 

 with ascorbic acid its lifetime cannot be infinitesimally small. The 

 concept that an Fe-^02 compound may be able to act as a dehydro- 

 genating agent has been discussed in Chapter VIII. 



Coupled oxidation of hemochrome and ascorbic acid. The catalysis 

 of the oxidation of ascorbic acid by hemochromes has been studied 

 by Barron and co-workers {IS^), but they failed to notice the accom- 

 panying oxidation of the hemochrome, which had previously been 

 observed by Karrer and co-workers {1J^69). In fact, under the 

 conditions of their experiments a great part of the catalytic action 

 on ascorbic acid oxidation must have been due to the resulting verdo- 

 hemochrome (1697). Lemberg and co-workers {1697) confirmed the 

 view of Barron that ascorbic acid is oxidized by the hemichrome 

 formed b}- the autoxidation of hemochrome. The whole coupled 

 oxidation can thus be formulated as follows (where H2A denotes 

 ascorbic acid and A, dehydroascorbic acid) : 



Fe2+ + Oj -+ Fe=+ O. + H.A -^ Ye-^ • H,0, -^ verdohemochrome 



T 



' I I 



pg3+ < ' 



+H2A 



It can be considered as a peroxidative destruction of the porphyrin 

 nucleus in the ferrous hydrogen peroxide heme compound. Each 

 time only a small part of the oxygen compound reacts in this direction 

 (/3), the major part being transformed into hemichrome {a) and 

 reduced again by ascorbic acid.* 



* I use the occasion to correct several printing errors in two papers of Lemberg and 

 co-workers (1697,1698) that may have obscured tlie meaning. In Biochemical Journal, 

 32, 15-2 (1938), Table II, the headings of the columns under "B. Method 2" differ 

 from those under "A. Method I." They were erroneously omitted and should read: 



Column 1, Ascorbic acid, mg.; column 2, Hemin, mg.; column S, Ratio, ascorbic 

 acid : hematin; column 4, Mg. ascorbic acid oxidised; column 5, Mg. ascorbic acid 

 which should be oxidised provided the ratio be 1:2; column 6, ditto, provided the ratio 

 be 1:1; and column 7, % reaction of theoretical (1:2). 



Page 149, line 7 read: "the methene group a instead of "one of the Qf-methene 

 groups." Page 180, line 13: read "with the theory that," instead of "with the second 

 theory mentioned in the introduction, that." 



In the same journal, page 180, line 25: read "557 m/x" instead of "527 ni/x" and 

 line 29: read "ferrous" instead of "ferric." A few other misprints should be readily 

 corrected. 



