THE EFFECT OF BETA RADIATION ON PORPHYRIN COMPOUNDS 



Considerint^ now the general efTect of /3 radiation on the porphyrin 

 molecule, it may l)e seen, firstly, that there is no essential difTerence between 

 the elTect of irradiating protoporphyrin in plasma and irradiating it in 

 aqueous solution [Figure J, I, II and III). That is, there is a rapid conversion 

 to a cyclical tetrapyrrole {i.e., a porphyrin) having a Soret band with an 

 extinction coefficient which is approximately 90 per cent that of proto- 

 porphyrin. The product porphyrin, moreover, is not affected by radiation 

 at the strength used. 



This is consistent with the phenomenon reported by Rothschild, Cosi and 

 Meyers^, who worked with ferriprotoporphyrin, and by Hamilton, Okada 

 and Morrison^, who worked with lactoperoxidase. Thus the conversion to 

 the product porphyrin takes place, irrespective of whether the porphyrin is 

 free, part of a haem or part of a haemoprotein. 



There are general reasons for considering that the product porphyrin (or 

 porphyrin moiety) is of the oxyporphyrin type, i.e., that it is formed by 

 replacement of the CH group of one of the methene bridges with a C — OH 

 or a C=0 group (reference 5, p. 91) and these reasons have been previously 

 given*. 



However, as a result of their work with ferriprotoporphyrin, Rothschild, 

 Cosi and Meyers conclude that the vinyl groups of the porphyrin side chains 

 are responsible for the change. They base this on two main considerations. 



(1) Ferrideuteroporphyrin, which lacks the vinyl groups of the ferri- 

 protoporphyrin does not exhibit a similar behaviour on irradiation. 



(2) On irradiation, the absorption band of the ferriprotoporphyrin which 

 is centred at 612 m[j., shifts to 600 m^i. One would infer from this a change 

 in the structure of the porphyrin side chains. 



The present investigation, being primarily concerned with protoporphyrin 

 compounds, did not include investigation of deuteroporphyrin compounds, 

 hence no comment can be made on this aspect. 



With regard to (2), however, it may be seen from Tables 1 and 2, that in 

 the present investigation there was no band shift on irradiation, either with 

 protoporphyrin or with ferriprotoporphyrin. This suggests that there was 

 no alteration in the side chains. Lemberg and Falk^" found that any altera- 

 tion in side chain structure caused a definite band shift. Furthermore, the 

 decrease in strength of all bands in both compounds suggests a saturation 

 of the methene bridge bonds. Also, Rothschild, Cosi and Meyers obtained 

 their band shift when the spectra were examined in NaOH solution. The 

 general instability of the band positions of ferriprotoporphyrin in NaOH 

 solution is well known; Lemberg and Falk^", for instance, quote only the 

 hemochrome band positions when referring to haems. 



Further, if the figures given by Rothschild, Cosi and Meyers for the 

 pyridine hemochromes of their solutions are examined, the band position 

 changes following irradiation are very small and do not suggest a definite 

 alteration of the side chains. These figures are given in Table 3 in which the 

 band positions for the pyridine hemochromes of ferriprotoporphyrin, as 

 quoted by Lemberg and Legge^ Rothschild, Cosi and Meyers^ and the 

 present investigator, are given. The band positions for the pyridine hemo- 

 chromes of the product substances of Rothschild, Cosi and Meyers, and of 

 the present investigator, are also given. 



100 



