253 



Keelin T. Fry and Anthony San Pietro 



ratios of absorbance in the visible region to that in the ultra-violet region 

 (277 mjj) for the absorption maxima at 330 mp, 420 mjj and 465 mp are 0. 81, 

 0. 62 and 0. 57 for the methaemoglobin reducing factor and 0. 65, 0. 49 and 

 0. 44 for PPNR. In each case, the values for the methaemoglobin reducing 

 factor are about 1. 27 times the corresponding value for PPNR. This differ- 

 ence is most probably due to the fact that the methaemoglobin reducing factor 

 is devoid of tryptophane ' ' whereas PPNR contains one mole of tryptophane 

 (Table 2). The presence of tryptophane in PPNR is indicated by the shoulder 

 in the absorption spectrum at 290 mp which is absent from the absorption 

 spectrum of the methaemoglobin reducing factor. In addition, there is a 

 shift in the position of the minimum at 295 mp in the spectrum of the methae- 

 moglobin reducing factor to 305 mp in the PPNR spectrum. 



Fig. 1. Absorption spectra of 

 methaemoglobin reducing factor 

 from parsley and PPNR from 

 spinach. Upper curve , methaemo- 

 globin reducing factor, 0. 77 mg of 

 protein per ml; Lower curve, PPNR 

 equivalent to 0. 081 micromole of 

 iron per ml. 



400 500 



WAVCLENGTH , m^ 



Recently, Katoh and Takamiya ^ ) reported the isolation of PPNR from 

 Brassica campestris (Komatsuna). The absorption spectrum of the Brassica 

 PPNR corresponds almost identically to that of the methaemoglobin reducing 

 factor from parsley. The relative absorption values at 276, 330, 420 and 

 465 mp are I. 00, 0. 81, 0. 60 and 0. 54 for the PPNR from Brassica . These 

 correspond very well with those given above for the methaemoglobin reducing 

 factor. We would suggest, therefore, that the PPNR from Brassica will also 

 be found to be devoid of tryptophane. 



In view of the difference in tryptophane content of these various proteins, 

 any comparison of their ultra-violet absorption spectra per unit of protein 

 will be meaningless. However, the absorption in the visible region per 

 micromole of iron should be comparable provided the iron in these proteins 

 is an essential constituent of the chromophoric group(s) and that the chromo- 

 phoric group(s) in these proteins are the same. The absorbance per micro- 

 mole of iron per milliliter at the wavelengths of the absorption maxima in the 

 visible region is presented in Table 1. For the purposes of comparison. 



