Ferrihaemoprotein Hydroxides 1 25 



calculated from an equation corresponding to (8) or (9) is found to be 0-93. 

 The fraction of the high-spin form is thus 0-07. Absorption spectra for the 

 high- and low-spin forms based on the extinction coefficients of ferrimyoglobin 

 hydroxide and this peroxidase hydroxide are plotted in Fig. 14 where it can 

 be seen that they are very similar to those in Fig. 13. The spectrum of the 

 low-spin form follows that of the root peroxidase derivative very closely, as 

 would be expected with apg,. having a value so near that of unity. In this case 

 the extinction coefficients in the region 600 to 650 m/^ have small positive 

 values, with no corrections being applied. The band maxima occur at almost 

 the same wavelengths, with extinction coefficients very similar to those 

 obtained before, as shown in line /of Table 4. 



With the previous value of a^b = 0-5, these absorption curves can be used 

 to calculate the spectrum of ferrihaemoglobin hydroxide, with the result 

 shown in Fig. 15. The agreement is quite satisfactory, the shoulder at about 

 600 m/i being reproduced very well. 



The absorption curve for ferrileghaemoglobin hydroxide can be used in a 

 slightly different way. Making the assumption that this is entirely the low- 

 spin form, the spectrum of the high-spin form can be obtained from either 

 the ferrimyoglobin or the ferrihaemoglobin data as shown in Fig. 16. These 

 spectra compare very favourably with those for the high-spin form in Figs. 

 13 and 14. The slight shift in the wavelengths for maximum absorption, and 

 the small variations in extinction coefficients (see lines g and h in Table 4), 

 are to be expected in view of the systematic displacement of the bands of 

 ferrimyoglobin derivatives relative to those of ferrihaemoglobin noted 

 previously. The spectra in Figs. 14 and 16 show very clearly that the main 

 absorption bands are not very dependent on the low-spin values chosen for 

 the magnetic moments of the root peroxidase and leghaemoglobin hydroxides. 



The Ultra-violet Region, 300 to 480 m^ 



Inspection of the curves for the fluoride and cyanide derivatives in Fig. 8 

 shows that those for ferrimyoglobin are displaced by 4 to 5 m/i towards the 

 red and have lower extinction coefficients throughout the Soret band region, 

 380 to 440 m/<. The ratios of Soret band maxima, Cnb/^Mb' ^^e 1-06 and 1-10 

 for the fluoride and cyanide derivatives respectively. It is not surprising 

 therefore that calculations using the extinction coefficients for the two 

 hydroxides taken from Fig. 1 1 , with no corrections to allow for these systematic 

 diff"erences, give absorption spectra for the high- and low-spin forms which 

 show none of the expected features. A narrow band is obtained for the low- 

 spin form having a maximum at 412 m/* with e^^ = 112, in contrast to a 

 very wide band for the high-spin form, having a maximum at 418 m/i with 

 ^niM = 88 broadening out to a shoulder at 400 m/t with e^^ = 75. 



Repeating the calculation, but correcting for the wavelength displacement 

 by a factor of 5 m^a, and for the diff'erences in intensity by multiplying the 



